Hi Sharon!
Lye concentration vs. water discount can be a very confusing topic. On the surface, they seem to be talking about the same thing, but they are actually two different animals when you get down to it.
When people speak of a
lye concentration, they are talking about the
strength of a solution that is made up of lye and water (i.e. how much lye is in the solution in relation to the water amount).
For instance (I gleaned this from another forum):
a 25% lye solution = 25% lye + 75% water (the water weight is 3 times the weight of lye)
a 33% lye solution = 33% lye + 66% water (the water is double the lye weight)
a 40% lye solution = 40% lye + 60% water (the water weight is 1.5 times the weight of the lye)
a 50% lye solution (only for the very experienced soaper) = 50% lye + 50% water (half and half)
What this means is that I'm taking the water amount of
any given recipe and adding enough lye to it to bring it to a certain percentage of strength. When I tell someone I used a 33% lye solution, they know immediately that I used twice as much water as lye, no matter what recipe I happen to be using. It's pretty cut and dry and standard as compared to
water discounts, which can be pretty nebulous.
For instance, if I tell someone I used a 33%
water discount, they'd want to know what the foundational amount of water is that I am discounting from. Here's where it gets tricky because not all
lye calculators on the net base their water amounts on the same criteria, even if it's the same exact recipe. A 33% water discount at So & So's does not give you the same water discount percentage as Whatchamacallit's because So & So's bases their water amount on oil weight, and Whatchamacallit's bases theirs on lye weight. It's not uniform across the board. A 33% water discount could mean one thing here and another thing there because they are both starting with different water amounts based on different criteria.
Lye solutions, on the other hand are very standard and mean the same thing across the board no matter what your recipe is. For instance, A 33% lye solution
always means twice as much water as lye for every single recipe no matter how different it is from another recipe.
Hopefully, that makes sense.
Well, with that out of the way, you are now probably wondering what difference the various lye solutions make in your soap. Well, pretty much in a nutshell, the lower your lye concentration, the longer your soap will take to trace and the longer it will take to harden up and evaporate all the excess water out after unmolding. The higher the concentration, the faster things go and the faster your soap hardens and drys out after unmolding. The highest I've gone is 40%. It was for a Castile-type soap with 80% Olive Oil in it. I wouldn't go higher than a 33%, though, until you have a good feel for soaping and all of the curves it can throw you. Things move really fast the higher you go, so it's best to gain confidence at the lower levels first.
SoapCalc's default Lye concentration is set at 31%, I think. I like 33%. It's a nice middle of the road percentage. Not too low, not too high, and my soaps don't shrink much at all as they are curing in comparison to those made with a lower lye concentration. This especially comes in handy when making Castiles, because they can be quite soft at first if a low lye concentration is used. My very first Castile-type was done at a 26% lye solution, and it took a week for it to even be hard enough to unmold! Then it took at least 3 months more to harden up enough to use it without it completely turning to jelly! When I make the same recipe now, but use a 33% lye solution instead of 26%, I can unmold it within 12 hours and it reaches the same hardness at 2 or 3 days that it took my first batch to reach in 3 months! It's amazing!
Well, I hoped that helped!
IrishLass
