Oil Slick on Top of Slab Mold Soap

[Elysium]

Hello folks,

Another question from someone who has been soaping for a while, but have had burning questions that I've never known the answer to:
Whenever I use my slab mold (it's acrylic), there is a thin puddle of oil on top. Now, if I leave the soap in the mold for a few days, it reabsorbs, and the soap ends up turning out perfectly as long as I'm patient.
But why does this happen??!!
It's the same recipe that I use in my silicon/wood log mold, and I never have this type of problem.
Does anyone have any ideas? I'm glad the soap turns out, but I'd rather not deal with this!
Thanks,
Andi/Elysium

 

[topofmurrayhill]

If we go with the theory that you're getting some separation of the oil and lye, it could be because you're doing a lighter trace to swirl the slab, or because the temp ends up being lower and there's more time to separate. These things would be exacerbated by softer recipes and/or higher water amounts. If this is minor separation, the soap could come out okay but the top and bottom of the bars would be somewhat different if tested.

 

[Susie]

Do you CPOP? If so, overheating can cause an oil slick for a few days.

 

[Elysium]

Honestly, it could be either.

I don't do CPOP exactly, but I do warm my oven for a few minutes, then turn the oven off, and keep it in there to cool rather than wrapping it up.
I remembered, in talking to my husband, that we made homemade pizza that night, so, for the first time ever I took the soap out and put it on a heating pad. I bet it overheated at that point.
But since I was swirling, I did swirl at a lower temp, lighter trace, without a water discount. So, maybe it was the perfect storm.
Sadly, this is the first time this happened that I ended up throwing the batch out. It just did not seem to want to re-absorb the oil. Oh, well...
Thank you folks for helping me think this through. It helps. A lot.

 

[Susie]

When I say it can cause an oil slick for a few days, I truly mean it. I had one take a whole week to get to where I could cut it. That soap was HARD when it got cut. But worth it. I learned a lot on that batch.