Master batching formula help

[grettastith]

I know that most people master batch their lye & water at 50/50. What is the formula for the additional liquid.

I have my go-to recipe that I master batch for, so when its time to use the mixture I just measure it out--but I KNOW a formula exists that would make this fairly easy.

I used to be pretty decent at algebra but apparently the heat has made my brain soft because I cannot for the life of me figure out the formula.
If this is the wrong forum for this question, could someone please point me in the proper direction?

I apologize for such a basic question. I'm confident the members on this forum will know the answer...the members here are smart, talented, generous and of course, some of you are VERY experienced...

Thank you in advance for your help!

 

[DeeAnna]

Look at your recipe. Find the alkali (lye) weight for the batch. Find the total water weight for the batch.

Multiply the alkali weight by 2. That is the weight of 50% lye solution to use.
Subtract the alkali weight from the total water weight. That is the weight of additional water to add.

Example --
Alkali weight = 397 grams
Total water weight = 863 grams

50% lye solution weight = 2 x Alkali wt = 2 X 397 = 794 g
Additional water weight = Total water wt - Alkali weight = 863 - 397 = 466 g

 

[AliOop]

.... OR use SoapmakingFriend as your lye calculator, and check the master-batched lye option. Then enter the ratio of MB lye solution (usually 50%), enter your recipe oils and batch size, and voila. The additional liquid will be figured for you.

 

[Carly B]

I know you didn't ask, but I masterbatch my lye at 2:1, water:lye, so it's all ready to go when I need it. I rarely use liquid other than water (I use powdered GM in my soaps, added directly to the oils), so should I want to make a soap using aloe or a brine soap, I'll just mix the lye separately for those.

For Christmas, when I'm making soap for gifts, (I don't sell), I'll masterbatch my favorite oil blend, so anytime I want to make a quick batch of soap, everything's ready and all I need to do is decide the mold, fragrance, and colors. This also allows me to easily make small (like 1 or 2 bar) batches to test fragrance/color with a minimum of fuss.

 

[TheGecko]

Look at your recipe. Find the alkali (lye) weight for the batch. Find the total water weight for the batch.

Multiply the alkali weight by 2. That is the weight of 50% lye solution to use.
Subtract the alkali weight from the total water weight. That is the weight of additional water to add.

Example --
Alkali weight = 397 grams
Total water weight = 863 grams

50% lye solution weight = 2 x Alkali wt = 2 X 397 = 794 g
Additional water weight = Total water wt - Alkali weight = 863 - 397 = 466 g

And this is why I make a 'ready-to-use' Lye Solution.

I know that most people master batch their lye & water at 50/50. What is the formula for the additional liquid.

Addition and Subtraction.

To make a 50 oz batch of my recipe at 33%, I need 9.54 oz water + 4.70 oz NaOH = 14.24 oz - 9.40 oz (50/50 [4.70*2]) = 4.84 oz additional liquid.

 

[DeeAnna]

Since I often use alternative liquids such as beer or aloe for the "extra" water, a 50% NaOH solution makes the most sense for me. I'm willing to put up with the minor inconvenience of a tiny bit of math to gain this flexibility