castile calculations

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ohsoap

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I apologize in advance if this has been covered before but I couldn't find it in any of the threads. Tomorrow I am making my first 10lb batch of soap in my new mold. I am doing a bastile to see what bar sizes I will get out of it, but I know from doing my regular 2lbs, that my castiles don't fill the mold because of the water disc. Is there a special formula to calculate how much oils will actually fill the mold?

I'm wondering if I should take my recipe at the defaulted WD in soap calc, then with the 40% lye concentration, and figure out the difference, and just keep upping the oils until I get the same number (volume) between oils and water total. (I hope that makes sense)
 
I have read that post several times, and I do use the l x w x h x .40 method when figuring out oil amounts per mold.

I have a new large slab mold and want to do a castile soap to test out the bar sizes that it produces for me. I am going to be doing a bastile recipe (so I don't waste any of my good oils/butters) my lye solution will be 40%, but that means I will have less liquid volume then I would normally to fill the mold. (I know this from doing castile in my reg 2lb batches).

edited to add:
Here is what I've done: I took my regular amount of oils and water total 165.6 and subtracted the new amount 143.166 = giving me a difference of 22.43 oz
Soap calculator says that my water % of oils is 19.3 % so I subtracted that from the differnce of 22.43, that gives me a total of 18oz more oil. I put it in soap calc and my water and oil total are only off by 1oz.
 
You may have to adjust your multiplier (the 0.4) to suit your water discount.

BUT by the end of the cure period (especially the long cure that OO soaps require) your discounted soaps will shrink less. So you need to take that into consideration as well.

I'm sure there is some calculus genius who can figure out what dimensions you will end up with if you pour a certain depth and cut certain length bars and such and end up with a particular surface area that loses water during the cure at a certain rate... but I'm not that person bob knows!
 
I saw another calculator that actually used .38 rather than .4 perhaps that either accounts for some of what you said, or simply doesn't round where the .4 one does.

Just a thought.
 
Oh actually you just need algebra, I think - not calculus.

You CAN use the specific gravity of your individual oils to calculate a general SG for your formula. Then use that and the % lye solution you want to use to get the specific gravity of your total batch. Use THAT number to convert to volume (which will shrink) per weight.

Figure out how full you want your mold to be and convert those measurements to volume.

Then use your two answers to figure out how much soap batter you need and back-calculate to how much oils you need.

A bit of a pain, perhaps, not impossible.

Or you could just try 0.38...
 
found my answer on another forum:

A batch made with a 40% solution and a batch made with a 33% solution, both batches using the same weight of oils, will be different sizes in the mold.
The difference will be how much water you used.
There will be a bit of difference in the finished and cured sizes of bars.
If it's important to you that the bars be the same size, ie, they both pour to say 2½ inches high in your mold, then you
will need to use a slightly higher amount of oils (and lye) in your batch.
If your old batch recipe is a total raw weight (oils, water, lye, fragrance) of 5 lbs and your new batch recipe, using a
stronger solution rate - 40% rather than 33%, is 4.5 lbs, you can work backwards to make the new stronger solution
batch weight equal the original size of 5 lbs. You add more oils, water and lye until the finished batch weight is 5 lbs on
paper. Lost yet? ***

Don't forget to run everything through a reputable lye calculator and re-calculate your new recipe for the additional oils/lye.
 

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