pH monitoring in CP soap

[chachalaca]

Hello, has anyone studied the pH in their soap from the day made throughout the curing process? I just started monitoring mine with a calibrated electronic pHmeter. I was assuming I would have a curve going downwards, since the reaction of lye and oils would cause the pH to tend more to neutral, but instead I got this, each color is a different type of soap, the X axis is the time (in days), the Y axis is the pH. I can't understand the sudden jumps! So I am not sure if the method I am using to meassure is not right, if this behavior is normal or if there could be other things affecting the reaction? Thanks for any light you can throw on this!!

 

[shunt2011]

You don't state how you are testing the soap but here's some information on how to test the PH properly. I don't test PH. I only zap test for active lye. Soap can range from 8.5-10.5 or up to 12 and be perfectly safe.

https://www.modernsoapmaking.com/how-to-ph-test-handmade-soap/

 

[DeeAnna]

Soap will never have a "neutral" pH, meaning a pH of about 7. It will always be alkaline (pH above 7). Assuming you're testing your soap using a correctly diluted solution of soap and distilled water at constant temperature, the pH readings are as I would expect -- a slight trend downward for the first few days and then stabilizing in the 9-11 pH range. The pH of other soap might be a bit higher or lower than yours, but not greatly so.

"... I am not sure if the method I am using to meassure is not right..."

Uh, so what is the procedure you use? You don't say anything about it, so how can we give advice?

Speaking in general, I'd say the unusually large spikes are most likely calibration errors or procedural errors. Soap pH doesn't naturally jump around like that. The minor variations you see up or down by a few tenths of a pH unit are quite possibly normal variations. If you don't have a lab quality pH meter, this much variation could be typical for your equipment.

 

[IrishLass]

Ditto what DeeAnna said.

Barring some of the huge jumping variations due to probable equipment issues, at least things aren't too way off, generally speaking. By that I mean that it's at least keeping within the alkaline range. That is good, because soap, by its very definition, is 'an alkaline salt of a fatty acid', so you can be certain its pH will always rest on the alkaline side of the pH scale. Anywhere from 8-something to 12-something is completely normal (for example, Johnson's sells a baby soap with oatmeal with a pH of 12.35 that rates very low on the irritability index scale).


IrishLass

 

[chachalaca]

Hello! Thanks for all your comments!! They are very, very useful.

Sorry I did not describe the testing method: I add 1 g of soap in 99 ml of distilled water (at room temperature), agitating until it dissolves and then meassuring with an Orion bench pH meter.

shunt2011: thank you for that very, very useful link!!

I am meassuring this out of mere scientific curiosity in an attempt to learn a little bit more about my soaps and how they behave throughout the curing process . In the end they all appear to be aiming towards the same pH between 9.9 and 10, which is the expected.