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Chemist question re: glycerine rivers/stearic streaking

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newbie

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Oh soapy chemists! I know you are out there and we have at least a few.

I have a question re: the difference between glycerine rivers and stearic streaking. I have thought they were the same thing, caused my stearic acid separating out during heating but someone else is thinking stearic streaks are made from Stearic Fatty Acid, and are white opaque spots that have solidified/saponified quicker than other FAs, but glycerine rivers are made with titanium dioxide and glycerine molecules from triglyceride and are transparent little rivers.

Can you shed some light on this? I would like to make sure I've not got wrong info in my head and am always up for learning something new.
 

galaxyMLP

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Stearic Spots/streaks:
Ok, my understanding is that stearic spots are white spots in the soap. This leads me to believe that the stearin in lets say palm oil, is doing something hinky in the soap.

Oils are comprised mostly as triglycerides and not as free fatty acids. Stearin is the triglyceride of 3 stearic acid molecules. :)

I actually think that stearic spots are not caused by a faster reaction but from the solution of lye/oils cooling too fast causing the stearin to solidify into fatty little blobs. In this case, it would react slower with the lye. Either way (reacting faster or solidifying out and reacting slower), it makes white spots b/c it wouldn't solidify w color.

Glycerin Rivers:
Sometimes when soap overheats, and its pretty much done with saponification, it will separate into glycerin and soap. Now the question: why doesn't the glycerin stay liquid?

I have a theory that becasue glycerin is a solvent for soap, it actually solubleizes the soap around the separated glycerin and gets enough soap into the separated glycerin to "harden" it withough loosing transparency (think MP soap here).

I think that some pigments may tend to overheat the soap more easily and that's why it's evident when you add them. It also happens with more water. My thought about this is that the glycerin separates from the rest of the soap more easily if it also has more water. The glycerin and water will likely separate from the rest of the soap together. More water + glycerin, more likely to separate, more likely for glycerin rivers.
 
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newbie

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Why would the water separate from the soap? Is it because glycerin is hydroscopic? If that's the case, I would think the glycerin would have to separate out first and then draw water to it. Or not? Stearic streaking doesn't always seem white but perhaps it's because sometimes people are calling glycerin rivers stearic streaking. Why wouldn't stearic hold color at all and be only white?
 

DeeAnna

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I dug up some stuff I've written before. Here ya go:

"Glycerin rivers" and "stearic spots or streaks" are misleading terms. The more generic terms "streaking" and "mottling" are really more accurate. Any soap can show rivers, streaks, spots, or mottling; these patterns are just more obvious in soaps with pigment colorants.

Probably the worst name of the two is "glycerin rivers" because it is so incorrect. A high concentration of glycerin would make soap soft and goopy, and the soap should wear away more quickly in those areas due to the softness and water solubility of the glycerin. Ask yourself -- have you ever seen a "glycerin river" that behaved like that??? "Stearic streaks" or spots can be formed by non-stearic soaps as well as stearic soap, but that term is closer to reality.

I have no illusion that people are going to use more accurate names, however. "Glycerin rivers" and "stearic spots" will continue to confuse and mislead soapers for decades to come.

***

Soap is made of many different kinds of soap molecules. As the soap cools in the mold, some parts of the soap may crystallize (harden) before other areas do. That affects where a colorant such as titanium dioxide ends up in the soap. Colorants are more likely to concentrate in the soaps that crystallize last. Also some of the soaps themselves are more opaque (stearic, palmitic) and some are more translucent (oleic, linoleic), which in itself can cause mottling and streaking even without added pigments.

Water content is not really what causes mottling and streaking, although I can see why one would think it is. What water content DOES do is affect whether the soap is likely to gel or not at relatively low temperatures. High water soaps go to full gel at much lower temps than low-water soaps, so they are thus more likely to show mottling and streaking than soaps that don't gel.

Mottling and streaking is more likely if the soap reaches a full gel state and is allowed to very slowly cool, so the different soaps (stearic soap, oleic soap, palmitic soap, etc.) can crystallize at different times.

***

The old soap makers (1800s to early 1900s) intentionally made mottled soaps that were popular with the customers of the day. A mottled soap could only be made using a pure soap that had not been "filled" or adulterated with too much water, clay, or other cost-cutting additives, so the mottling was proof the soap was pure and high quality. The soap maker would add a coloring agent to a finished soap, pour the soap into "frames" (large molds), and carefully control the rate of cooling.

The stearic and palmitic soaps would solidify into pale colored clumps first, essentially concentrating the color into the remaining liquid oleic and linoleic soaps. When the oleic soaps solidified, the color would be trapped within these areas and make rivers or veins of darker color around the stearic clumps. The size and appearance of the mottles were controlled by the oils in the recipe, the way the finished soap was handled, and the rate of cooling in the frames.

"...When [soap] is permitted to cool rapidly the colouring matter remains uniformly disseminated throughout the mass; but when means are taken to cause the soap to cool and solidify slowly a segregation takes place: the stearate and palmitate form a semicrystalline solid, while the oleate, solidifying more slowly, comes by itself into translucent veins, in which the greater part of the coloured matter is drawn. In this way curd, mottled or marbled soap is formed..."
Source: http://www.1911encyclopedia.org/Soap
 
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galaxyMLP

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Aannnd I was very wrong. Thanks again Dee Anna. I should probably just avoid answering these types of questions in the future. I'll probably send around all kinds of mis-information... oops. I was at least on the right track w/ spotting due to cooling.
 

not_ally

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"Mottling and streaking is more likely if the soap reaches a full gel state and is allowed to very slowly cool, so the different soaps (stearic soap, oleic soap, palmitic soap, etc.) can crystallize at different times."

D, based on the above: if you like to gel via CPOP, do you think it would it help in avoiding mottling to CPOP (I usually do it for an hour or so at 150) and then put it in the freezer/fridge to cool more rapidly?
 
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MrsSpaceship

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The old soap makers (1800s to early 1900s) intentionally made mottled soaps that were popular with the customers of the day. A mottled soap could only be made using a pure soap that had not been "filled" or adulterated with too much water, clay, or other cost-cutting additives, so the mottling was proof the soap was pure and high quality. The soap maker would add a coloring agent to a finished soap, pour the soap into "frames" (large molds), and carefully control the rate of cooling.

The stearic and palmitic soaps would solidify into pale colored clumps first, essentially concentrating the color into the remaining liquid oleic and linoleic soaps. When the oleic soaps solidified, the color would be trapped within these areas and make rivers or veins of darker color around the stearic clumps. The size and appearance of the mottles were controlled by the oils in the recipe, the way the finished soap was handled, and the rate of cooling in the frames
Oh my word, described that way, it sounds absolutely beautiful. Does anyone make soap like this still? I mean on purpose as an actual controlled technique as you mention rather than accidental. I really rather like the oops soaps that I've seen with these characteristics.
 

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There was someone on here who was doing this on purpose and their soaps were fantastic. It was some time ago that they posted some though. When I have mottling, it always looks clumpy and rough but this person made the most beautiful things.
 

DeeAnna

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"... if you like to gel via CPOP, do you think it would it help in avoiding mottling to CPOP (I usually do it for an hour or so at 150) and then put it in the freezer/fridge to cool more rapidly? ..."

Not_ally -- I don't know the answer to that question -- you'll have to just try it and see. I have to say I'd be more likely to just put a fan on it at room temperature rather than put it in the fridge or freezer -- warm but moving air is more likely to get the core temperature down quicker than cold, still air. Think about how fast you chill down on a cool windy day in fall but how warm you can stay on a cold, still day in winter.

I do think a more important factor in streaking/mottling is water content due to how the amount of water affects the rate of saponification. More water => more tendency to go into gel for a longer time => greater chance of mottling. If you are soaping at "full water" you may have better luck avoiding streaking/mottling by using a less water in your soap. This is true even if you CPOP.

I used to soap at 33% lye solution concentration and didn't see any indications of mottling/streaking whether or not the soap gelled, whether I did CPOP, or whatever. I went to 30% to 31% lye solution concentration to get a bit more time to work with the soap batter. I routinely get mottling/streaking now in my soaps that go into gel (most do). You wouldn't think that slight drop in lye concentration would make a difference, but it has for my soaps. I actually rather like mottling/streaking, so it doesn't matter to me if my soaps are mottled or not.

You might find some excellent tips in Auntie Clara's articles on this subject:
http://auntieclaras.com/2014/05/glycerine-rivers-secret-revealed/
http://auntieclaras.com/2014/05/glycerine-rivers-trying-to-understand-them/
http://auntieclaras.com/2014/08/intentional-crop-circles-water-discount-as-a-design-tool/

"... Does anyone make soap like this still? I mean on purpose as an actual controlled technique as you mention rather than accidental...."

MrsSpaceship -- Not that I'm aware of. I gather even the old makers had trouble getting a consistent pattern of mottling, and the consumer preference for mottled soap eventually died out, probably to the relief of the soap makers who went to the trouble of making it. :) I'd look at Auntie Clara's articles for guidance if you want to develop a reasonably reliable method of mottling soap -- as I said above, I suspect control of water content and thus control of the rate of saponification is key to mottling.
 
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FlybyStardancer

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"... if you like to gel via CPOP, do you think it would it help in avoiding mottling to CPOP (I usually do it for an hour or so at 150) and then put it in the freezer/fridge to cool more rapidly? ..."

Not_ally -- I don't know the answer to that question -- you'll have to just try it and see. I have to say I'd be more likely to just put a fan on it at room temperature rather than put it in the fridge or freezer -- warm but moving air is more likely to get the core temperature down quicker than cold, still air. Think about how fast you chill down on a cool windy day in fall but how warm you can stay on a cold, still day in winter.
Not to mention that you would be heating up the food in the fridge/freezer, potentially putting them into the danger zone for bacterial growth!
 
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