I typically masterbatch the NaOH all by itself. IMO the NaOH beads I have are harder to work with than my KOH, which comes in flakes that don't jump around with static electricity. Not to mention I'm only using a few grams of KOH per batch for bar soap. It's not nearly the hassle of working with NaOH.
But that's purely a personal preference -- there's no real reason why you can't masterbatch the two alkalis together as one mixture. Just be sure you get the proportions right. If you're also making a masterbatch at 50% concentration, remember the amount of water you use needs to be equal to or larger than the total weight of alkali (NaOH + KOH).
If the math is daunting, you can trick a soap recipe c@lculator to do the mathy part. Here's how --
Create a "recipe" using a calc that allows the user to create dual lye (also called hybrid) recipes. Soapmaking Friend and LyeCalc are two will allow this.
For example, I want to make a masterbatch at 50% lye concentration. I want to use 1 kg (1000 grams) of NaOH to make this masterbatch. I want to make a dual-lye blend of 95% NaOH and 5% KOH.
Set up the proportions of NaOH and KOH. For my example, I'm using 95% NaOH and 5% KOH.
Decide about how much NaOH you want to use to make the masterbatch. This is your "target" weight. I'm going to use 1000 g NaOH to make my masterbatch.
Set up the lye concentration (or water:lye ratio) to be the concentration you want for the masterbatch. I will enter 50% lye concentration. This is the same as a 1:1 water:lye ratio.
Create a recipe using one fat. I'm going to use coconut oil.
Set the superfat to zero percent (0%). All the other settings don't matter.
Set the starting weight of the fat at some number. It can be any number you like -- just pick something. I'm going to start with 2000 g coconut oil.
Calculate the recipe. Look at the calculated NaOH weight. Is the calculated NaOH weight at your target weight? My target is 1000 g NaOH and the calculated NaOH for 2000 g of coconut oil is a lot lower than my target NaOH weight.
If not, increase or decrease the weight of fat and recalculate the recipe. I went up ... a lot ... to find the answers I wanted.
Repeat as needed. When the calculated NaOH weight is equal to the target weight, you're done.
Use that weight of NaOH, the calculated weight of KOH, and the calculated weight of water to make your masterbatch.
The screenshot shows the results for my example. I used
https://www.lyecalc.com/ to do the calculations.
