Size of soap and cure time.

[ellaphantcy]

I know that the cure time involves 3 different phases to take place: saponification (which takes 24-48 hours), drying (which takes longer but can be affected by different techniques), and misc. cure stuff (pH changes, etc.) which is basically just a waiting game.

I also know that cure time tends to be hotly debated within and amongst soaping forums, so I'm not trying to start any fires here, but I was wondering if, from a scientific perspective, the size of the bar affects the various chemical reactions that take place during cure time, and if it then indirectly affects cure time.

I would assume that the surface area to volume ratio plus exposure to different environmental variables would make a difference, but I searched far and wide and couldn't find any information on it.

If anyone could shed some light on this, that would be great. I'm constantly on these boards, but this question has been bugging me lately so I finally caved in and joined. Thanks!

 

[Susie]

I have no proof, other than my own experience, so take this for what it is worth. However, it is easily testable, so you can do the testing yourself.

I have found that although the larger surface area of thinner bars does hasten drying quite a bit, it does not affect "cure". Soap still improves after it is "dry". I tested this by cutting a loaf into slices that are wider than the previous one by 1/2 inch. So, the first two bars were 1/2 inch, the third 1 inch, the fourth 1 1/2 inch, etc to the 3 inch mark. I then tested every bar once a week (I only tested one 1/2 inch bar at the time. I cut two in case the first one melted away before I finished testing.) All of the soaps felt the same at each week of test. The 2-3 inch bars were still slightly damp in the centers when I concluded the test at 12 weeks, but they were "cured" and the quality of the soap was not changing noticeably after the 8 week mark. This test took one batch of soap, but it taught me far more about what happens to soap than anything else.

 

[DeeAnna]

Wow, Susie! Nice work -- thank you for sharing!

 

[shunt2011]

Yes, thank you for sharing your experiment and you observations.

 

[The Efficacious Gentleman]

That is interesting. Of course, usually the dry phase can finish before/around the same time as the 'misc' phase, but it is good to know that they aren't totally linked.

Did the damper bars still last a short time than the dry ones?

 

[Susie]

Please remember that I live in a high humidity area. I was trying to determine the proper length of cure time when I did that test. YMMV depending on your climate.

 

[The Efficacious Gentleman]

Absolutely- but the fact that it can be 'cured' from the point of view of lather/mildness and so on before it is fully dried also suggests that when it is dry it does not necessarily mean it is cured from the point of view of lather/mildness and so on. Very intriguing and thanks again for taking the time to note it and post it

 

[Susie]

That is interesting. Of course, usually the dry phase can finish before/around the same time as the 'misc' phase, but it is good to know that they aren't totally linked.

Did the damper bars still last a short time than the dry ones?

I just saw this, sorry. I cut the largest bars in half and let them dry out before using after I concluded the test. But all of the bars were noticeably smaller after each subsequent wash for 4 weeks, then they stopped trying to melt away each time.

 

[ellaphantcy]

Thanks so much Susie! It's crazy to me that cure time can be so impervious to different variables, but your experiment really cleared up a few things for me.

 

[Susie]

Cure time has to be the hardest thing for folks to learn that can't be changed about soaping. It is the number one thing newbies ask about, so don't feel alone.

I really do encourage you (and everyone else) to do that for yourself. Once you go through testing each bar each week, you then KNOW what proper cure is, and exactly when your soap hits it. I would also encourage newbies to do weekly weighing of a bar when it is tested so they can see how fast an uncured bar can melt away compared to a properly cured one.

 

[DeeAnna]

This thread might be helpful: http://www.soapmakingforum.com/showthread.php?t=35831