Why does soap get milder with time?

[Ianto]

I understand that water is evaporating during cure time which makes soap harder. What I don't understand is why soap would get more mild when it cures. If I had to make a guess it would be something along the lines of glycerine being more evenly distributed as time goes on.

Does anyone have an explanation for why soap gets milder with time?

 

[serfmunke]

I thought I read or heard that after 48 hours the soap is as mild as it gets and then the water is the only thing that changes. BUT I do dream a lot and have a difficult time differentiating between my dreams and reality. Kinda like a 4 year old

 

[new12soap]

I do, in fact, have an explanation. It is a similar principle to wine, or cheese. The soap is soap within a few days, but there is still a lot more going on chemically than just water evaporation. There is a drop in pH every week, most notably between weeks 4 and 6. It is "cure time", the soap is curing, not just "drying time", there is a lot more going on in there than just losing water. Fresh cheese is still cheese but has nowhere near the depth that a well cured cheese has.

 

[jcandleattic]

I thought I read or heard that after 48 hours the soap is as mild as it gets and then the water is the only thing that changes. BUT I do dream a lot and have a difficult time differentiating between my dreams and reality. Kinda like a 4 year old

you must have been dreaming on this one. LOL
Soap is sooooo much milder after a good long cure than it is at 48hours.
and no, there is much more going on during the cure time than just water evaporation. So very much more.
Try a soap (hp or cp - doesn't matter) at 48 hours, then try a soap from the same batch at 4 weeks, then again at 2 months, 6 months and then a year.
You will be amazed at the differences you feel...

 

[Seifenblasen]

If you are into science, the pH actually continues to drop for 60 days out of the mold:
http://cavemanchemistry.com/WaterDiscount-Dunn.pdf

If you prefer a more "artistic" explanation, please see new12soap's answer.

If you believe in anecdotes, more than once I have "new" soaps I don't like, set them aside, forgot about them, and dug them out a few months later because I was out of soap, and was surprised by how nice they were and wondered why I did not like them in the first place.

 

[Ianto]

Thanks everyone for the answers. Seifenblasen or anyone else - is this Alkali/ppt NaOH part per trillion, thousand, or per part... I am not accustomed to seeing pH described this way.

 

[Seifenblasen]

Oh, the parts per trillion (ppt) has to do with hydronium and hydroxide ion concentration which affects the pH. For example, water has a pH of 7, is considered neutral and has an equal number of hydronium and hydroxide ions. If you go up the pH scale (where things become more alkaline), the number of hydroxide ions increases.

 

[Hazel]

I like new12soap's "artistic" explanation. It's a creative way for answering Ianto's question. I personally have noticed I retain more information by conceptual descriptions/imagery drawn upon familiar items. I blame this on classes primarily chosen for art and humanities. Fortunately, we have examples of both types of explanations to help clarify information for the "scientific" members and the "artistic" members.

Mmm...cheese and wine.

 

[DeeAnna]

ppt = parts per thousand, not parts per trillion. At least in Dunn's writing. This way of expressing concentration is a little irregular in most of science and engineering, but it is convenient in the world of soap making.

For example, you'll see saponification values expressed as a decimal -- 0.136 -- and as a whole number -- 136. The second figure can be expressed as 136 ppt -- meaning 136 parts NaOH by wt are required to saponify 1000 parts of a particular oil, again by weight.

Expressed in words, pH is the base 10 exponent, expressed as a positive number, of the hydrogen ion concentration in a solution. If [H+] = 10^-7 then the ph = 7

Here's a related thread: http://www.soapmakingforum.com/f11/expediting-curing-process-32831/

 

[Seifenblasen]

Parts per trillion.

 

[DeeAnna]

I agree that "ppt" means "parts per trillion" elsewhere in engineering and science. Dunn's book is another matter.

In your reference to Section 8.7 in Dunn's book, please note he does not use the abbreviation "ppt" to refer to parts per trillion. He spells the units out in words.

Throughout the rest of his book, he does use ppt, but as an abbreviation for parts per thousand, not parts per trillion. He defines the abbreviation clearly on page 24: "...A question phrased this way gives its answer in parts per thousand, or ppt...."

So, for example, his standard soap recipe, Duckbar's Delight, has this formula: Olive390 Coconut280 Palm280 Castor50 Lye288 Aq144. The number after each name is the ppt -- parts per thousand -- of each ingredient in the recipe. The numbers after the oils add up to 1000, so a recipe of Duckbar's Delight using 390 g olive, 280 g coconut, etc. will have exactly 1000 grams of oils.

The Lye288 is the amount of a 50:50 mixture of sodium hydroxide and water (aka a 500 ppt NaOH solution). Dunn adds extra water (Aq144) to dilute the 500 ppt master solution to the concentration he wants for the recipe.

--DeeAnna

 

[Miz Jenny]

I do, in fact, have an explanation. It is a similar principle to wine, or cheese. The soap is soap within a few days, but there is still a lot more going on chemically than just water evaporation. There is a drop in pH every week, most notably between weeks 4 and 6. It is "cure time", the soap is curing, not just "drying time", there is a lot more going on in there than just losing water. Fresh cheese is still cheese but has nowhere near the depth that a well cured cheese has.

THANK YOU!

 

[Seifenblasen]

I am not accustomed to seeing pH described this way.

Not trying to interpret Dunn's book in its entirety, not trying to muddle the question with SAP values or clay structures, etc., was simply answering the question that pH can be expressed in terms of hydronium and hydroxide ions concentration, in parts per trillion.