Puzzled by Purple edges on soap

[glendam]

I recently made a lot of soaps (for me), about 50, all in one evening In different molds. I am curious why the first loaf shows some purple spots on the edges. They were all made from the same oils master batch with the same lye water solution master batch. The colorants were also the same except for the white portion, the first soap was made with Titanium dioxide and the rest with Winter white mica. Same fragrance too.
The main difference in the making was that the first soap thickened up fast because of the TD. The rest stayed fairly fluid. My guess is that the first one went through gel phase and the others may not have. (40% lye to water concentration). I heated up the oils to about 105 F and lye water was at room temperature
The recipe includes lard, olive oil, coconut oil, Shea butter, castor oil and mango butter. I used EDTA and ROE.
any ideas?
In the picture

the two soaps on the left are from that first batch.

 

[AliOop]

Wow, that is really interesting! Did your lard have any BHT in it, by chance?

I have seen some mentions of "pinking" due to BHT, and sometimes from coconut oil.

 

[Ford]

Silicone or paper lined mold? How long since you used that particular mold? Can't tell top or bottom.

 

[glendam]

@AliOop
Good point! I had thought about the pinking I had read about, and now that you mention it, it is possible that combined with the blue of the soap it made purple. I don’t see BHT in the label (Armour Lard) but I see BHA. Perhaps it is similar?

INGREDIENTS: LARD AND HYDROGENATED LARD, BHA, PROPYL GALLATE AND CITRIC ACID ADDED TO PROTECT FLAVOR.

@Ford
It is a silicone mold, nurture soap 5lb loaf mold. It has been a while (about 6 months) since I used it last. Initially I thought it might be some Sharpie marks I had made on it, but the location of the spots (inside the soap along cutting lines) Made me discard that thought.

 

[AliOop]

Yes, my understanding is that both BHT and BHA can cause color changes in highly basic (high pH) environments. EDIT: I'm not sure the part about high pH is correct; I just read some additional references where the color changes came from acids or salts.

If you type "pinking from bha or bht" into your Internet search bar, it will pull up scientific articles which mention color changes when exposed to different chemical. Most of them are behind paywalls, but even the previews will give you some info about that.

 

[dibbles]

I use Armor lard, and don't have the problem, but I have read about it. If your lard percentage was high, that would be my guess too.

 

[mx5inpenn]

Same fragrance too.

Sometimes fragrances cause discoloration like this. I have one in particular that I love, but is masculine and discolors a pretty lavender sometimes. You think one gelled, so heat may effect discoloration

 

[glendam]

@mx5inpenn this is a good point and perhaps a contributing factor. I used The Perfect Man FO, which does say that discolors to lavender, though it never had done it for me before and I have used it often (normally does go through gel phase). Thanks!

@dibbles it was about 30% of lard in the recipe. It does not seem too high to me but perhaps it was high enough, thanks!

 

[dibbles]

@dibbles it was about 30% of lard in the recipe. It does not seem too high to me but perhaps it was high enough, thanks!

I don’t think that is so high. I was thinking if it was more in the 75%+ range. Sometimes soap just does naughty things, and you may never figure out what caused it. The soap is still very pretty.

 

[dmcgee5034]

I have no ideas to add but had to comment on how lovely your soaps are @glendam
Beautiful work

 

[glendam]

@dmcgee5034 Thank you! I really appreciate that. I tried doing the one pot wonder but with the first loaf it was too thick to achieve it.

 

[DeeAnna]

I think this "pinking" from BHA or BHT depends on pH, temperature, and other factors. The color can range anywhere from pink/lavender to yellowish and sometimes even to turquoise. Pinking is going to happen from time to time in soap when these antioxidants are present, but from what I see here on the forum, it's pretty rare. So I'm not sure it's a problem that a person should worry too much about trying to prevent.

If you're into reading academic papers, here's one that talks about this issue. It's related to the presence of BHA or BHT in plastics, but the chemistry applies to soap as well. Yellowing and Pinking of White PE/PP | AMPACET CORPORATION

 

[glendam]

Thank you for sharing that paper @DeeAnna! very interesting