# costly math mistake



## SE18 (Feb 21, 2008)

I wasted nearly 2 lb of RTV, actually QSI Quantum Silicates' QM130T (quantumsilicones.com) by not knowing basic math, which I'm really poor at and admit. I'm using a scientific scale, measured in grams.

The mixing cup is 14 grames. The instructions call for 10:1 mix ratio with the catalyst. I figured 90% weight for the silicone and 10% for the catalyst, subtracting the weight of the mixing cup then adding it back in. (I am not concerned with a specific quantity, I only need to know what the formula for doing it is, and perhaps an example using my 14 grams would be helpful.

If anyone is good at math, please help!

Dave V


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## Dick413 (Jan 7, 2008)

wouldn't 12.5 grams of silicone and 1.5 grams of hard work? i don't think the weight will work because 
of different wgts. of silicone and hardener base.


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## Fritz (Jan 11, 2008)

Note: An US pound is only 453,5 Gramms (0,453,5 KG)


Have Fun

Juergen / Fritz


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## SE18 (Feb 21, 2008)

thanks, I was hoping to get a formula. As I mentioned, specific weight is not what I'm after, but an example would help (with the formula). Sorry for being so picky.


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## Dr Rivet (Jan 5, 2008)

Dave 

Usually mix by VOLUME not weight. If the ratio is 10 to 1, that means 10 UNITS [whatever you measure in be it mils or ounces] to 1 UNIT of the other stuff; TOTAL 11 UNITS 

Example: 

Suppose you have two containers that will measure up to 16 fluid ounces [1 pint]. Fill one with 10 ounces of the RTV, pour it in the mixing container. 
Use the other measuring container and fill with 1 ounce of catalyst. Pour that in the mixing container. mix the stuff up; you have you 10 to 1 ratio. 

Good luck on your project 

Maybe a casting guru will jump in here and tell you a simple way to do it.


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## SE18 (Feb 21, 2008)

Thanks, so my mistake was using 10 units (9 and 1) vice 11 units. Using Dick's example and working backwards, what would the formula be? Lets assume I'm not measuring each separately. 

For instance, I'm gonna put the silicone in the mixing cup and then add the catalyst, so I need an aggregate number (to avoid using 2 cups to measure, less cleaning). Did that make sense?


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## chuck n (Jan 2, 2008)

Part of the problem is that in our use of English weights and measures, ounces are both a measurement of weight and a measurement of volume. In the metric system they are separate. Grams is the unit of weight and liters is the measure of volume. 

So if you are measuring something in ounces, you need to know beforehand whether the instructions are for weight or volume.


Water (distilled) has a density of 1 and 8 ounces of water (weight) has 8 ounces (volume). Other liquids such as gasoline have a density that is less than one, so 8 ounces (weight) of it would over flow aa 1 cup measuring cup (8 ounces (volume).



Another problem with our system is that there are two kinds of ounces used for weight. An ounce of gold is heavier that an ounce of lead or feathers. Gold is weighted in Troy ounces, 12 troy ounces to a pound. Lead and feathers are measured in Avoirdupois ounces, 16 to a pound.

Chuck 


Make it easy on your self and go the the supermarket and buy a plastic measuring cup that has both ounces and milliliters along the side. Use one of those graduations for your measurement. I think that the milliliters would be easier.


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## kormsen (Oct 27, 2009)

it is either 9.1 parts plus 0.9 parts. (or 90.909% plus 9.091%) 

but for me its normally 10 to 1 shotglasses....


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## jbwilcox (Jan 2, 2008)

I think a 1:10 dilution means 1 part and 9 parts to make a total of 10.

At least that is what I have always used.

John


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## eheading (Jan 5, 2008)

If I were doing it, I would just do it in 10 gram increments. Put 10 grams of the RTV in, and then add 1 more gram for the catalyst. Makes it real easy.

Ed


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## jamarti (Jan 2, 2008)

I believe you need to forget the grams thing. That is weight. 10:1 is expressing a ratio. 10 units of something to 1 unit of something. and Yes, you end up with 11 units of material. Think of the gas/oil ratio mixes for 2 cycle engines. If the requirement is 50:1. You buy the little bottle of oil at 2.6 (2.56) fluid oz and mix it with 128 fluid oz of gasoline. You end up with 130.6 fluid oz. of mixture. You would not weigh the gas and put in 1/50 of the weight of oil because oil and gas do not weight the same. 

Or another way...if the school required a ratio 10 kids to one teacher or a 10:1 ratio. you end up with 11 people. 

You would not need any scale to weigh anything. 10 dixie cups plus one dixie cup of hardener. or 10 shot glassses plus one shot glass of hardener. or use the little plastic cups for ketchup ard salad dressing available from a restruaunt supply.


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## SE18 (Feb 21, 2008)

John just mentioned 9 and 1, which I did (parts). Hmmm. 

I think I'm not clearly explaining myself. All solutions thus far involve measuring the catalyst separately. Here's the sequence: 

14 gram cup (whatever oz that is) 

Fill, lets say, with 150 grams of solution. 

Question 1: 

What should the TOTAL weight now be of all 3 items on the scale: cup = 14 grams; solution = 150 grams; catalyst = x 

Question 2: 

What's the formula and/or procedure/algorythm for that? 

If anyone can answer these 2 questions, that would suffice. See, I told you it's hard!


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## tmtrainz (Feb 9, 2010)

In all my experience when mixing something by ratio, such as 10:1, you take ten parts of A and mix with one part of B for a total of 11 parts. No need to complicate it more than that. 

In your situation, 150 g container with part A in it minus 14 g container = 136 g solution (part A). 136g/10 = 13.6 g (part B). Using same container, 14g plus 13.6 g part B = 27.6 g total container plus part b. 

I hope that helps. Remember, keep it simple. I'm sure someone will chime in and way overcomplicate the situation, which they already have done.


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## SE18 (Feb 21, 2008)

thanks, this is what I needed!


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## chuck n (Jan 2, 2008)

Lets go back to basics. Forget about grams and ounces. Deal only with volume. The only math required is multiplying the volume of the catalyst by 10. If you have 10 fluid oz of A you need 100 fluid oz of B. In metric 10 ml (milliliters) catalyst would require 100 ml of resin.


First, add the two numbers. If it is 10:1 the total is 11, not 10. If it is 1:1 (as we see in many of the epoxies at the hardware store) the total is 2, not 1. Fortunately, most epoxies are fairly forgiving. You will probably get reasonable results with 9:1, 10:1 or 11:1. There may be some applications where this is critical, but there is a little slop in most of these reactions. The biggest effect may be in curing time. Too much catalyst may speed up the reaction, and too little may slow it down.


By the way, 14 grams is about 1/2 oz. 


Chuck


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## Tom Parkins (Jan 2, 2008)

Now it really depends on if you are mixing for 1:29 or1.20.3. Depending on the scale that you are working in you will need to adjust the proportions. Since your container is 14 grams and you started this post on the 14th you need to wait until this thread is completed and then subtract the number of days that it ran and divide by the number of post in this thread. Multiply that by the average number of posters on MLS then take the square of sum of the average age of the posters. This should then tell you how much hardener you need to subtract to make the problem simpler. Thanks for asking, the members of this forum are always glad to be of assistance.










Tom


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## jbwilcox (Jan 2, 2008)

I'm a Medical Technologist and have worked in the lab for 30 years.

Unless I have been doing it wrong all those years, here is the correct way to make a 1:10 dilution

take 9 parts diluent and add 1 part sample. That makes a 1:10 dilution.

A 1:5 dilution is made by taking 4 parts diluent and adding 1 part sample

If you take 10 parts diluent and 1 part sample you are actually making a 1:11 dilution.

In reality in most cases the difference between a 1:10 and a 1:11 dilution may not be significant

But this is one subject that I know a little about so I just want to set the record straight on how to make dilutions.

John


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## SE18 (Feb 21, 2008)

I'm really confused now! But thanks for input anyway. Guess I'll wait to see who else might chime in with what exactly 1:10 means (or 10:1) 10 total parts or 11?


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## SteveC (Jan 2, 2008)

Posted By jbwilcox on 14 Feb 2011 10:51 AM 
I'm a Medical Technologist and have worked in the lab for 30 years.

Unless I have been doing it wrong all those years, here is the correct way to make a 1:10 dilution

take 9 parts diluent and add 1 part sample. That makes a 1:10 dilution.

A 1:5 dilution is made by taking 4 parts diluent and adding 1 part sample

If you take 10 parts diluent and 1 part sample you are actually making a 1:11 dilution.

In reality in most cases the difference between a 1:10 and a 1:11 dilution may not be significant

But this is one subject that I know a little about so I just want to set the record straight on how to make dilutions.

John
John

Really not trying to argumentative, just trying to understand, how would your explanation work in a 1:1 mixture?

The way I see it you're talking about taking a whole and diluting it. Where as in creating a resulting whole mixture at a ratio of 10-to-1 it has to be additive (i.e. 10 x-units + 1 y-unit = 11 total units). For example when I think of water i.e. H2O that's a ratio of 2 parts hydrogen combined with 1 part oxygen that results in one whole molecule of water, a whole comprised of three units at a two-to-one mixture ratio.


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## chuck n (Jan 2, 2008)

John:

If you want a 20% solution you cut it with 4 parts of water(which would be 1:4, not 1:5). In this case you are adding 1 part and 10 parts, so the dilution factor is 1/11 instead of 1/10.

The best analogy so far is mixing the oil and gas for a 2 cycle engine. The instructions on the pre-measured oil bottle is to add the oil to 1 gallon of gas. For a 1:32 mixture, you add 4 fl oz of oil to 128 fl oz (1 gallon) of gas.

Chuck 

By your example, when the instructions say to mix equal amounts the ratio should be 1:2 rather than the 1:1 we commonly see on most epoxies.


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## Pterosaur (May 6, 2008)

Wow, I think we have sent this poor guy in circles...It is a Mix ratio. Look at the label, it is critical to get this right...Does it say "Mix by weight" or "Mix by volume"? You cannot interchange these two. 

Either way, eheading had it right...Mix 10 units of one with 1 unit of the other for a 10:1 ratio. Your total will be 11 units.


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## tmtrainz (Feb 9, 2010)

Now it really depends on if you are mixing for 1:29 or1.20.3. Depending on the scale that you are working in you will need to adjust the proportions. Since your container is 14 grams and you started this post on the 14th you need to wait until this thread is completed and then subtract the number of days that it ran and divide by the number of post in this thread. Multiply that by the average number of posters on MLS then take the square of sum of the average age of the posters. This should then tell you how much hardener you need to subtract to make the problem simpler. Thanks for asking, the members of this forum are always glad to be of assistance. 

That's good!!! I like your logic...lol. Chuck N is correct in saying that a little bit more or a little bit less of the catalyst (hardener) will only change curing time. Remember, we're not trying to glue the heat-resistant tiles to the bottom of the space shuttle.


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## jbwilcox (Jan 2, 2008)

A 1:1 dilution is not diluted!! It is just that simple.

A 1:2 dilution is 1 part diluent and 1 part sample.

You are not being argumentitive, just asking for help in understanding dilutions.

I guess you could take the word of others, but as i said, I am a Med Tech and make these types of dilutions every day. If I were doing it wrong, do you think I would still have a job?

But then you are free to accept the advice of anyone you want. It is a free country, I guess

John


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## SteveC (Jan 2, 2008)

Posted By Pterosaur on 14 Feb 2011 11:25 AM 
{snip...}[/i] It is a Mix ratio. Look at the label, it is critical to get this right...Does it say "Mix by weight" or "Mix by volume"? You cannot interchange these two. {snip...}[/i] By weight. QSI QM130T Data Sheet[/b]


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## tmtrainz (Feb 9, 2010)

The following procedure should be followed for obtaining optimal performance 
from the QM130T. 
Charge 100 parts, by weight, of QM130T and 10 parts, by weight, of the chosen 
catalyst into a clean, compatible metal or plastic container. Shake the catalyst well before 
use. The volume of the container should be 3-4 times the volume of the material to be 
mixed. This allows for expansion of the siloxane material as it de-gasses. 

That is from the tech sheet. Mix 10:1. 100 parts to 10 parts by weight, for 110 total parts.


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## Semper Vaporo (Jan 2, 2008)

Posted By jbwilcox on 14 Feb 2011 11:42 AM 
A 1:1 dilution is not diluted!! It is just that simple.

A 1:2 dilution is 1 part diluent and 1 part sample.

You are not being argumentitive, just asking for help in understanding dilutions.

I guess you could take the word of others, but as i said, I am a Med Tech and make these types of dilutions every day. If I were doing it wrong, do you think I would still have a job?

But then you are free to accept the advice of anyone you want. It is a free country, I guess

John


Is this a terminology error? When I see the term "mix it one to one" I assume it means fill one container with part 1 and then fill another identical container with part 2. If it says "mix two to one" then I assume fill the first container twice for every fill of the second container. In the 1st instance I would have 2 container's worth of combined materials and in the 2nd instance I would have 3 container's worth.

But is the short hand notation of "1:1" and "2:1" the same meaning? I am of the understanding that John says it is NOT the same, whereas I admit that I thought they meant the same thing. For many products I bet it doesn't make a lot of difference; such as mixing oil and gas for a 2-cycle engine, or mixing consumer grade epoxies to put a lampshade back together, but maybe if it were for a medical product where my life depending on it being "right", or if an error in mixing might produce an explosively unstable product, then maybe it does make a difference!

Do the manufacturer's of consumer products know whether the average consumer has any idea which is meant if they use the short hand notation? I fear I might be in the majority of the unwashed masses who have assumed the two numbers seperated by a colon are the quantities/weights of the two products to be combined (and I have always worried about which number represents which of the 2 components!)


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## SE18 (Feb 21, 2008)

Posted By tmtrainz on 14 Feb 2011 11:57 AM 
The following procedure should be followed for obtaining optimal performance 
from the QM130T. 
Charge 100 parts, by weight, of QM130T and 10 parts, by weight, of the chosen 
catalyst into a clean, compatible metal or plastic container. Shake the catalyst well before 
use. The volume of the container should be 3-4 times the volume of the material to be 
mixed. This allows for expansion of the siloxane material as it de-gasses. 

That is from the tech sheet. Mix 10:1. 100 parts to 10 parts by weight, for 110 total parts. 

-------------------------

So the advice given by tmtrainz holds true now that you've found the data sheet.

The quantities would change if they were by volume and not by weight?


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## chuck n (Jan 2, 2008)

Solution ratio
strength concentrate:water

100% 1:0 (no dilution) 

50% 1:1 
33.3% 1:2
25% 1:3 
20% 1:4 
10% 1:9 

Chuck


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## SteveC (Jan 2, 2008)

Posted By jbwilcox on 14 Feb 2011 11:42 AM 
A 1:1 dilution is not diluted!! It is just that simple.

A 1:2 dilution is 1 part diluent and 1 part sample.
OK John, let's see if I've got this correct.
[*] A 1:1 dilution, means that the resulting solution is 100% sample and 0% diluent.
[*] A 1:2 dilution, means that the resulting solution is 50% sample and 50% diluent.
[/list] So if I wanted the resulting solution to be 90.9% sample and 9.09% diluent. Would that be noted as 1:1.011 or somewhere close to that?


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## jbwilcox (Jan 2, 2008)

Steve,

You are correct: 1:1 is 100% sample

1:2 is 1 part Sample and 1 Part diluent.

It seems like people want to tell me I am wrong on this, but I promise you I am correct.

Often people talk about a 1:1 dilution. They are actually referring to a 1:2 dilution.

A 1:3 dilution is 1 Part Sample and 2 Parts Diluent.

Please do not question me on this, for once in my life on this forum, I KNOW THAT I AM RIGHT AND IF ANYONE TELLS YOU OTHERWISE, THEY ARE WRONG, NO MATTER HOW SMART THEY THINK THEY ARE OR HOW INSISTENT THEY ARE THAT I AM WRONG.

I may not know a lot about trains, but I do know how to make a dilution.

John


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## jbwilcox (Jan 2, 2008)

A 20% soluton is the same as a 1:5 dilution. 1 Part sample and 4 parts diluent.

I know many of you think you are smarter than me about this, but I know who is right and who is wrong.

John


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## SE18 (Feb 21, 2008)

ok, I've got to run to catch my train (VRE), but I'll be back tomorrow to check on this for the definitive word, whatever that might be.


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## jbwilcox (Jan 2, 2008)

Lets complicate things even more:

Suppose you already have a 1:4 dilution but you now want to make a 1:8 dilution. How are you going to do it?

Of course you could start over from scratch and take 1 Part sample and add 7 Parts diluent to ge a 1:8 dilution.

The way we would do it in the lab is like this:

take 1 Part of the 1:4 dilution (which now becomes your sample) and add 1 part diluent to it. You now have a 1:8 dilution.

I know Dilutions, some of you know trains and I do not argue with you when you tell me something. 
John


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## chuck n (Jan 2, 2008)

Is it possible that they do things differently in the medical profession?

My dad was a college chemistry professor, and all I know is that if is screwed this up I'm in for one **** of a scolding when we meet up again across the "Great Divide".

Chuck


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## tmtrainz (Feb 9, 2010)

I spoke with my forensic chemist sister and she told me that in the world of chemistry John is truly correct in his stated method of performing dillutions. In the world of mixing epoxies, gasoline/oil, and in this case a two-part silicone compound use the simple method of for example: 10 parts A to 1 part B for a total of 11 parts. I won't say any more...I promise. 

Sorry to doubt any one. Not trying to start a riot. 

Tom


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## chuck n (Jan 2, 2008)

I guess that I'm going to be in trouble with dad as far a chemistry dilutions go, but I'll still mix my epoxy in equal parts, 1:1

Chuck 


The bottom line is that if we were going to make a 10% nitric acid solution (yes I know that it would really be a 6.5% solution) we would both do it the same way. 1 part nitric acid and 9 parts water. It is just that we would write it differently. I would say 1:9 and you would say 1:10. You sum the parts in the last number and I sum the parts outside the ratio. We end up with 10 parts total either way.


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## SteveC (Jan 2, 2008)

Well first off...

John, if you mistook my question _"So if I wanted the resulting solution to be 90.9% sample and 9.09% diluent. Would that be noted as 1:1.011 or somewhere close to that?"_ as an off-handed derogatory comment on you statements being correct, it wasn't, the question was in earnest.

In my limited layman's understanding...
[*] In modeling when we refer to the real full sized prototype we use the statement of proportion of 1:1 (i.e. this being a statement of equality). And if we were to build a model to this scale proportion, what we'd be doing is building an exact full-sized duplicate of the original.

[*] When we refer to building a model to a size something less in size than the prototype, by convention we place the reference to the prototype on the left and the reference to the model on the right, for example a proportion of 1:2. When completed, the model will be exactly 1/2 the size of the original prototype.

Which is the exact same thing John was stating, because the resulting solution would be diluted by 50%, or half the strength of the original sample.

[*] If we desired to build a model larger than the prototype, then I believe it would by convention be proper to express the scale proportion as say 2:1. Where the reference to the prototype is now on the right and the reference to the model is on the left. And when built the model would be twice the size of the original. Although I'm not absolutely sure, I believe it would be mathematically correct to express it as 1:0.5 also, however, with the introduction of decimal numbers it becomes more cumbersome and the reason for the change in convention.
[/list] In the case of Dave's (i.e. SE18) original question the stated mixing ratio/proportion is 10:1 by weight. I believe the use of weight instead of volume is chosen because temperature comes into play, and volume can vary because of temperature, whereas weight will remain constant, in addition to the fact that accurately measuring weight is easier.

I agree with the method describe by tmtrainz...

 Select a container large enough to hold enough to make the mold (i.e. 3 to 4 times the volume of materials to be mixed, see page 3 of data sheet).
 Determine the tare (i.e. empty) weight of the container.
14 g

 Pour in enough QM130T silicone into the container to make the mold.
 Determine and write down the combined weight of silicone and container.
150 g

 Calculate the weight of the silicone alone by subtracting the container's tare weight from the combined weight.
150 g - 14 g = 136 g

 Calculate the required weight of catalyst needed, divide silicone weight by 10
136 g / 10 = 13.6 g of catalyst

 Determine weight of empy container.
14 g

 Calculate combined weight of catalyst and container.
14 g container + 13.6 g of catalyst = 27.6 g combined weight

 Place empty container on scale and carefully pour catalyst into container until combined weight is reached.
27.6 g

 Double check everything is ready to proceed.
 Combine silicone and catalyst as per Mixing & De-aeration instructions on page three of data sheet.
 Mind your working time as per Catalyzed Properties Table on page two data sheet.


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## jbwilcox (Jan 2, 2008)

I give up!

I don't know how many times I have to say it, a 1:9 dilution is not the same as a 1:10 dilution.

Sure, when you are just trying to get it "Close" then it probably does not matter. 

But to be Technically correct is another subject.

I would loose my job if I started mixing diltuions like some of you are talking about. 

It is really funny how people are so set in their ways that they refuse to listen to someone who has worked for over 30 years doing exactly that, making diltuions every day.

Today for example, I had a high WBC count that I could not report because it was beyond linear limits of the instrument. I made a 1:5 dilution (1 part blood, 4 parts Isotonic Saline) and ran the mixture and came up with a WBC count of 105,000. If I had done it the way some of you are suggesting, I would have provided the doctor with an inaccurate result, even though it would have been close to the correct number.

Sometimes, especially in formulating medications a small error like that can make the difference between life and death.

I guess I should haave used terms railroaders could understand.

You take red box car and mix it with 4 blue box cars and you now have 5 box cars. that is exactly the same as 1 part blood and 4 parts diluent, you end up with 5 total parts. How much more simple can i possibly make it?

I am finished with this discussion. You can all make your dilutions any way you want. 

John


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## chuck n (Jan 2, 2008)

One last comment and I'm out, too. Dilutions are not the same as mixing reagents. This whole discussion has been about mixing reagents. Parts is parts.


Chuck.


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## kormsen (Oct 27, 2009)

John is right. but that does not help. 

if one purchases "ten to one" (10:1) two-part mixtures one gets a container with ten parts plus one container with one part. so the agent is one out of eleven. but it is sold named as "10 : 1". 
(should better be called 10 + 1). 
so for practical aplication one adds a tentht of the weight/volume of agent to the weight or volume of the main stuff.


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## SE18 (Feb 21, 2008)

Hi I'm back. 

Chuck is right!!!! 

I'm not talking about the math (which I'm still going over); I'm talking about the forgiving nature of 1:10. 

The gooey stuff, which was supposed to cure in 16 hours, made it completely cured after day 2! Here's a small batch of what I did (some wheels and link and pin coupling) 

Hopefully the photo shows up. And, I'm back to reading what you wrote last night 










Dave V


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## SteveC (Jan 2, 2008)




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## SE18 (Feb 21, 2008)

Thanks Steve. I'm going to do what I should have done: contact the company. 

I have some other questions for them anyway. I'll post what they tell me. 

BTW, the tear strength on these molds is incredible!! I'm used to the 1:1 stuff, which rips a lot more easily. This stuff is almost impossible to tear. 

Dave


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## SE18 (Feb 21, 2008)

OK so the regional manager replied to my email. I asked him 2 questions, one about the 10:1 issue and another unrelated question I had about pouring lead/solder mixture into the mold. 

He only answered the second question (which was yes, you can do it). 

I supplied him a link to this forum. I can only surmise that after he read all of your replies, he decided to bow out of the discussion. (Or perhaps he didn't know the answer) 

So the mystery continues. 

Dave


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## Ironton (Jan 2, 2008)

OK guys, terminology. Unfortunately most US people do not use it correctly. Some of you are using "in" and some of you are using "to". 

A 1 in 10 solution is one part what you want and 9 parts solvent. You wind up with 10 parts of solution. 

A 1 to 10 solution is one part what you want and 10 parts solvent. You wind up with 11 parts of solution. 

As I said, most people blur the two. 1:10 is used to measure both types these days. Thus the chemist's claim of his practice. 

Hope this helps.


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## SE18 (Feb 21, 2008)

Rich, I'm going to split the different by doing this forumula "A 1 in/to 10 solution" 

In this way, I will get 1 part catalyst and 9.5 silicone (if my new math is correct).


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## msimpson (Jan 5, 2009)

Gentlemen, please -- 

When in doubt, follow the instructions -- here the recipe. The recipe http://www.quantumsilicones.com/PDFs/data/QM 130T Data Sheet.pdf says mix 10:1, silicone to catalyst, by weight. 

If your 2 lbs. was one batch, then two lbs. = 32 ounces -- add 3.2 ounces of catalyst. For one lb. = 16 ounces, add 1.6 ounces of catalyst. 

Prefer to do this in grams? 2 lbs = 908 grams, add 90.8 grams of catalyst. One lb = 454 grams, add 45.4 grams of catalyst. 

Using a 14 gram measuring cup? Well, at a half ounce, it is probably not holding two pounds, but let "S" = weight of the basic silicone in grams and "C" = weight of the catalyst in grams. Then S + 14 is the weight of the silicone in your mixing cup and S/10 + 14 is the weight of the cataylst in the cup. 

Given that there seems to be a lot of gassing and expansion when you mix, it doesn't look like you should add the catalyst into the silicone in the mixing cup. If this were not a problem, you could let T = total weight of cup and basic silicone. Needed catalyst is (T - 14)/10. Final weight of cup, silicone and catalyst = T + (T - 14)/10. 

Dave, feel free to send me a PM and I'll work specific numbers for you. Trust me, if you can work the molds, I can work the math. 

Best regards, Mike


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## SE18 (Feb 21, 2008)

"it doesn't look like you should add the catalyst into the silicone in the mixing cup." 

I'm not sure I get this. Then how would you mix it up? 

Thanks for the additional math and offer of help. 

Dave


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## msimpson (Jan 5, 2009)

Sorry, not in the measuring cup -- You mix them in the mixing bowl. (I have a BS in math, but I've spent a lot more time in the kitchen than the classroom in the last four decades.) I am assuming you are using a smaller measuring cup and mixing in a larger container. But maybe not -- I know zilch about casting, just a little about the math. Regards, Mike


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## Semper Vaporo (Jan 2, 2008)

You need a minimum of two cups, one for measuring the resin and one for measuing the catalyst. Then combine the two by pouring one cup into the other (or both into a third); there may be a prefered sequence of which is poured into the other. The idea is to not do the combining while trying to measure the proper amount of the 2nd ingredient.


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## SE18 (Feb 21, 2008)

I did it all in one cup on the scale, watching the digital meter as the grams increased and stopped when I got to the grams I was targeting. Pretty simple, don't see any downside.


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## Semper Vaporo (Jan 2, 2008)

Posted By SE18 on 15 Feb 2011 10:57 AM 
I did it all in one cup on the scale, watching the digital meter as the grams increased and stopped when I got to the grams I was targeting. Pretty simple, don't see any downside. 

I have no idea what the components you are combining are like, powder, chunk, thin or thick viscous liquid, etc. But depending on the components and what happens when they are combined you could miss-measure the volume or weight of the 2nd one. 

If it is a thick liquid, by the time you have the proper amount in the mixing cup, by measuring the weight, when you go to cut off the flow from the source container there could be small amount in the stream that would fall into the cup, thus increasing the quantity of that component in the mixture.

If there is a reaction when the two components meet, such that there is an out-gassing or vapor emission, then the amount of the 1st component might be reduced and thus, again, there might be too much of the 2nd component added to get the combined weight to the desired value.

Granted, when mixing epoxies for something other than the precision necessary for something that absolutely requires precision (like mixing epoxy for use in a life sustaining space craft assembly, medical procedure, crime detection, or scientific discovery) then a small amount of error in measurement is not a problem. With Epoxy it may just alter the working time with the mixture before it sets up. 

Also, the relative proportions might be inconsequential or not depending on the total amount being mixed. If you are only creating a few ounces of product, then the drip stream from the 2nd component might be more than the total quantity desired!


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## Mike Reilley (Jan 2, 2008)

Now...I gotta say, this has been a surprise dialog to me. NEVER have I seen a material that is mixed by weight...except concrete being mixed in a concrete truck. Pick one...plaster, portland cement, epoxy, paint, milk shakes, cakes, whatever...they're all put together by ratios of volumes of ingredients. Who ever saw a bag on Sacrete that says add 3 lbs of water to the contents of a bag?

In all my experience, with a lot of building materials, the mixing is done by a volume ratio...not a weight ratio. If this had been me, I would have mixed 10 parts by volume to 1 part by volume. I think the manufacturer should change his mixing instructions based on volume and NOT weight. Ya know, providing two measuring cups for this kind of expensive material doesn't seem like a cost prohibitive approach...one which holds one part by weight of the base material...and one that holds one part by weight of the catalyst...or just two cups with measuring gradients on the side.


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## Semper Vaporo (Jan 2, 2008)

Posted By Mike Reilley on 15 Feb 2011 01:11 PM 
Now...I gotta say, this has been a surprise dialog to me. NEVER have I seen a material that is mixed by weight...except concrete being mixed in a concrete truck. Pick one...plaster, portland cement, epoxy, paint, milk shakes, cakes, whatever...they're all put together by ratios of volumes of ingredients. Who ever saw a bag on Sacrete that says add 3 lbs of water to the contents of a bag?

In all my experience, with a lot of building materials, the mixing is done by a volume ratio...not a weight ratio. If this had been me, I would have mixed 10 parts by volume to 1 part by volume. I think the manufacturer should change his mixing instructions based on volume and NOT weight. Ya know, providing two measuring cups for this kind of expensive material doesn't seem like a cost prohibitive approach...one which holds one part by weight of the base material...and one that holds one part by weight of the catalyst...or just two cups with measuring gradients on the side.



The "home cook" measures by volume and this gives rise to the variability in the results (Why one cook's signature dish is another cook's... Ummm... disaster!)

A cup of flour? Is this prior to sifting or after, is it packed into the cup by scooping, or fluffed into the cup by pouring; do you strike it across the edge or scoop it down to the line printed on the side; is the "CUP" you bought at Wally*Whorled the same volume as the one I bought from the Antiques and Junque Shoppe?

A LARGE egg? Just what makes any one egg a "large one" (yes the FDA has standards) and how much variation is volume is there amongst a dozen "Extra Large" eggs? How old is the egg, the content evaporates through the shell over time?

A Teaspoon of a liquid or a "heaping" of powder will vary based on how shakey your hand is. And exactly how much is a "Heaping", anyway?

A "Master Chef" measures by weight which is much more accurate for proportions called for in the recipe and will help ensure the consistant results.

They measure concrete by weight in the truck because volume measurements of that much material is either too slow to handle or too inaccurate due to humidity changes.


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## Mike Reilley (Jan 2, 2008)

Posted By Semper Vaporo on 15 Feb 2011 02:04 PM 
....A "Master Chef" measures by weight which is much more accurate for proportions called for in the recipe and will help ensure the consistant results.

.



I'm not questioning that...but have you EVER seen on of those top shelf cooking shows where there's a scale around? I haven't. In fact, I hardly ever see them use any measuring device. And, being an engineer, when it says a cup of something...it's cup...not a shy cup, not a heaping cup...it's a amount that is level at the 1 cup line. Same with teaspoons and tablespoons of stuff. What good is having a measurement with variability if you're trying to be consistent.


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## Semper Vaporo (Jan 2, 2008)

Posted By Mike Reilley on 15 Feb 2011 06:18 PM 
Posted By Semper Vaporo on 15 Feb 2011 02:04 PM 
.... A "Master Chef" measures by weight which is much more accurate for proportions called for in the recipe and will help ensure the consistant results.

.



I'm not questioning that...but have you EVER seen on of those top shelf cooking shows where there's a scale around? I haven't. In fact, I hardly ever see them use any measuring device. And, being an engineer, when it says a cup of something...it's cup...not a shy cup, not a heaping cup...it's a amount that is level at the 1 cup line. Same with teaspoons and tablespoons of stuff. What good is having a measurement with variability if you're trying to be consistent. 

I watch a lot of those cooking shows on TV and I agree that I seldom see a scale, but I also have heard just about all of them (Julia Child, Mary Ann Esposito, Ming, Jacque Pepan, etc. sorry for mangling their names) comment at one time or other, often in an interview with some restaurant chef (demo-ing one of their signature dishs), that they would do most measuring with a scale instead of a by volume except when doing small batches. This is because the amount of error in volume/weight in small batches is less than in large ones; one component may compact more than another... such as 24 cups of flour could range all over the place in weight for that volume but the amount of liquid (milk, eggs, etc.) is a relatively stable proportional weight for any change in volume.

It is also quicker and easier to measure small quantities by volume than by weight.

I should emphasize that I WATCH those shows and seldom attempt to poison myself by duplicating the events portrayed on them!


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## Axel Tillmann (Jan 10, 2008)

Posted By Semper Vaporo on 15 Feb 2011 02:04 PM 

A "Master Chef" measures by weight which is much more accurate for proportions called for in the recipe and will help ensure the consistant results.

Actually the Master Chefs measure with his tongue!!!! Any ingredients list is just a guideline and no guarantee. (FYI - I know - I am trained chef - but do it only for hobby, friends, family, and my good customers who visit me once in a while







)

My wife always says, "can you mkae that dish again" and at no point in time will it be ever the same, like any Master Artist never made the same identical picture again. It is technically impossible. Each plant, each piece of meat, the humidity level, the..... you name it influence the outcome. Mastery comes from how to deal with that, including myself, since my taste changes too.

I can come close but never 100%.

However, there is an area in cooking where it is highly important - baking, that's basically a chemical science, and I don't do it well - I am more an Artiste









Of course too much of this







while cooking can change results too










I know this diverts from the original mixing question but I couldn't resist.


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## Loco Lee (Feb 17, 2010)

How Guys, 

Don't you go letting Axel clam that he does all the cooking up there. His wife is a good cook too. I should know, because she tried to fatten me up while I was up there. Everything they made was good, and now I'm going to have to go get something to eat, because I started thinking about their cooking, and now I'm getting hungray again. 

Loco Lee


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