Testing old lye

[B&E Homestead]

I have some pretty old lye that has never been opened but is hard and clumpy nonetheless. I guess the plastic container it came in wasn't sealed.
Is there a way to test it? Perhaps measuring the temperature change in the water when the lye is mixed into it? And if it doesn't get hot enough, does that mean less of the lye is reacting and I therefore need to use MORE lye per ounce of water?
I have made a few batches of soap with it and it does make soap but seems to take a long time to trace, like an hour, using an electric mixer like for cookie making. I'm fairly new to soapmaking so I'm not really sure how long is too long.

 

[TheGecko]

Good lye will quickly heat up to 225-250F. From what I have read, it should be used within a year of purchase.

 

[shunt2011]

I have had lye that's well over a year and works perfectly. If stored properly that is. I keep mine in the bottles they arrive in and then in a bucket with a gamma seal. I know several people have had lye years old that was still just fine if stored. Your may not as it's hard and clumped. I would probably call it a loss as moisture got into it and you don't know the strength of the lye at this point. Someone with more science knowledge will hopefully pipe in too.

 

[Lin19687]

There are a few older posts about this. I would search for it on Google to find the treads. Good answers there

 

[earlene]

How to test lye for purity:

 

[B&E Homestead]

Thank you for the video. That is very helpful. I am wondering now, what percentage of purity is still useable, and if my lye is below that percentage can I still make soap with it just using a little more lye? Like if my lye turns out to be 75% pure, I would assume that means it is 25% water. Is this correct thinking? My clumpy lye is still pure white, not grey. I'm pretty sure it is from moisture not from being exposed to air since the jars are unopened, just really old, maybe 6 years. It is from the lye guy, same stuff as in the video.

 

[earlene]

You would need to use a lye calculator that allows you to change the purity or be really comfortable with doing the math yourself. Not many here talk about doing the math themselves, although there are some who do and some who have developed their own.

One lye calculator that I know of DOES allow you to change the lye purity, but not with specificity.
https://calc.mendrulandia.es/
I think there are others that do allow adjustments for lye purity, I just don't recall which ones, not the ones I commonly use. I am sure I've seen one somewhere, but cannot find one now so maybe I mis-remember or it is defunct or I just can't find it.

EDIT: Aww, here is another that DOES allow user specificity for lye purity:
https://www.lyecalc.com/beginner-calculator
Maybe someone else will come along with more information or a link of one such calculator.

 

[earlene]

To compare the lye calculators that do not allow for lye purity adjustments, and the one that does allow for lye purity specificity (my second link above)

Here's what a 500 gram Castile soap would be like if I extend it to your scenario of 75% pure NaOH:

SoapBuilder (SoapmakingFriend): assumes unspecified purity - 63.65 grams of NaOH
LyeCalc: setting lye purity to 75% - 86.1 grams of your assumed tested 75% pure NaOH

So a huge difference in the amount of NaOH that you'd have to weigh out.

The other question that comes to my mind, is this: Is there an extra 22.45 grams of water in the 75% pure NaOH, that I would then deduct from the water amount for the lye solution? I would, yes. And it could make a lot of difference if it were a larger batch of soap.

 

[DeeAnna]

You can compensate for an NaOH purity less than 100%. The easiest way to do this is to tweak the superfat setting.

You want to reduce the superfat percentage by the difference between the assumed 100% purity and your actual NaOH purity. I know this is hard to understand when put into words, so here are a couple of examples --

My NaOH is 97% pure -- that's 3 percentage points below 100%.
I want my actual superfat to be 5%.
I'd set the superfat to 5% - 3% = 2%.

My NaOH is 75% pure -- that's 25 percentage points below 100%.
I want my actual superfat to be 8%.
I'd set the superfat to be 8% - 25% = -17%.
Yes, the number is negative -- you'd enter a minus 17 for the superfat setting.

 

[earlene]

Thank you so much for this information, DeeAnna! I am bookmarking this for future reference! You share such a wealth of information. I am so grateful you are so willing to do so.