Most seasoned soapmakers are well familiar with the phenomenon commonly known as glycerine rivers, TD (titanium dioxide) rivers, TD crackle or glycerine separation. The terms are all descriptive of what the phenomenon looks like: translucent rivers or streaks in a body of opaque soap. I’m not a chemist so I won’t attempt to give any conclusive explanation of the chemistry that goes into the formation of glycerine rivers, but when soap goes through gel phase, particles of colour pigment added to the soap seem to gravitate and stick to the greasy, water-repellent tails of the soap molecules while leaving the water-soluble heads of the molecules without pigment. This happens sometimes when soap coloured with titanium dioxide and other colour pigments goes through gel phase – but not always.
Soap with glycerine rivers is not technically inferior to other soap. However, the translucent ‘rivers’ are more water-heavy and will shrink more than other parts of the soap as water evaporates during cure. This can be seen as a slight indentation of the translucent areas. Some soapmakers like the look and ’embrace the rivers’, others think the rivers are ugly and some, like me, would just like to be able to understand the glycerine rivers so that we can make them happen or not make them happen as we please.
Over the years I’ve tried to read up on the reasons for glycerine rivers and I’ve asked more experienced soapmakers about it, but the only decisive answer I got was “it’s because of heat” and “don’t gel if you don’t want rivers”. Well, I wasn’t satisfied with that because I let almost all my soaps go through gel phase and sometimes when using colour pigments I would have rivers – but sometimes not. So yes, colour pigment and heat are prerequisites for glycerine rivers, but I felt there had to be more to the true answer.
Going over my own soaping history I often had glycerine rivers when I first started soaping. That frequency has decreased and I rarely have them at all these days. Interestingly other soapers have said the same thing. So what have I changed? Yes, I have tweaked recipes and I like to go with lighter trace than I did in the beginning, but the one big difference is water discount. In the beginning I would always use a lye/water ratio of at least 1/2.3. Now I regularly use a lye/water ratio of 1/1.4. So, my feeling was that it was water-related. I’ve been talking about this, but yesterday I decided to finally put my hypothesis to the test – properly.
To test the significance of water-content on the formation of glycerine rivers I had to rule out as many other variables as possible. I felt the best way to do this was to test it in one single batch. That way I could make sure that the oils, colour, fragrance and temps including ambient temp and meteorological circumstances were all exactly the same.
To keep my experiment as simple as possible I chose a very basic formula for my test soap: 20% coconut oil, 40% palm oil and 40% olive oil with a 5% superfat. Since I wanted to avoid anything that would cause acceleration of saponification I chose straight lemongrass eo for fragrance (I also anticipated ugly soap for home use and hubby likes lemongrass ). For colour pigment I used 1 tsp of titanium dioxide mixed with a small amount of glycerin for my batch of 1000g of oils.
I added the colourant and fragrance to the oils and stickblended carefully before adding the 1/1.4 lye/water solution which was warm but not hot. I stickblended the batter to very light trace. I then divided the batter into two identical jugs, weighing them to make sure that I had divided the batch exactly in half. Then, while stirring with a whisk, I added enough warm water to the one half for the lye/water ratio to be 1/2.4 in that half.
I wanted to ensure that both halves got equal heat. Since heat travels upwards I felt that placing one half of the soap on top of the other might jeopardize equality and so, using a lengthwise divider I poured both halves of the batch side by side in the same log mould and placed it in a 60C oven for 4h to ensure that the soap would go through gel phase.
I cut it this morning and yes, you guessed it, I wouldn’t have been doing all this talking if the results hadn’t been pretty spectacular! The same batch with the same oils, same amount of colourant, same fragrance and same external heat produced plenty of spectacular glycerine rivers on the water-heavy side but no rivers at all on the water-discounted side. The only other variable here except water content is that I hand-mixed the high-water half a little more than the low-water half to incorporate the added water.
So, for all of those who say “I’d love to get rivers but I don’t seem to be able” this is pretty good news. Just up the water and your chances will grow. And for those who say “I’m bummed because I want to force gel but my soaps are full of rivers” it’s equally good news: by doing a steep water discount you may be able to avoid them. What this experiment does not tell us is where the line is drawn; at what exact water concentration (heat, pressure, formula, fragrance, colourant etc being equal) do glycerine rivers start showing up? But that’s a different experiment and I will leave it up to somebody else 🙂
Nia
Wow, how interesting, this is pretty groundbreaking stuff!! Come to think of it, a lot of the soaps I have made with no water discount (florals typically) have been the ones I get ‘rivers’ in them, well this just proves it, if you want to avoid those rivers, choose a non accelerating fragrance and discount like mad! Thank you soooo much for sharing your experimentations, and your soaps are gorgeous too! 🙂
Yasmine
Thank you for doing this experiment. It has helped me a great deal.
Marie Descent
Thank you Clara for such an excellent post on the dreaded glycerin rivers! Your experiment was very well thought out and executed. And for sure, the results are indeed very telling. (You say you’re not a chemist, but you should be!) As with so many other soapmakers, I had also made the connection between heat and the formation of rivers, but never thought about the water component playing such an important part in the process. I will definitely put this new information to good use in my future soaping endeavours.
Thank you again and best regards.
Marie
Nancy
But??? If you do a heavy water discount won’t the soap be lye heavy???
Clara
Wether the soap is lye-heavy or not depends on the rate of lye to oils, not the rate of lye to water.
Shaman Lisa
Thanks for that clarification!
Clara
It’s a pleasure – as we say here in South Africa 🙂
Silvia
This is one of the most exciting posts I’ve read since I started making soap and blogging! Thank you for sharing your experiment and discovery. 🙂
I had glycerine rivers in one of my earliest soaps, but afterwards, I rarely had it. I hardly used TD during my first couple of months, and by the time I started using it, I had already increased my lye concentration to 33% from 28%. Nowadays I use a lye concentration of 37% or a lye/water ratio of 1/1.7. At this ratio, I almost never get glycerin rivers. If I did, it would just be minor streaks. I always gel my soaps as well.
Amy
Wow! Thank you for this!
M Mart
You are a genius! Excellent experiment. Thank you very much. 🙂
Kimberly H
Wow! I never would of made the connection to water. When I first started soaping I never once encountered rivers and I always soaped at full water. I often look at my older soaps with the colors so perfect and seamless and wonder, “What am I doing now?”. The only thing that is different from then to now, years later, is that I almost always use a water discount. It is now that I get rivers where I never did before. So in my case is backwards to your theory. Hmmm :/
Kim
In the experiment she uses titanium dioxide. Do You? I wonder if that might be why your results are different from hers?
Clara
Let’s keep in mind that rivers need a combination of conditions to happen. Without full gel phase you’re not going to have rivers – unless you have ricing in the batter which is a slightly different issue. Full gel phase is easier to avoid if you have less water in the batter, because the lower the water concentration, the higher the temp needs to be for the soap to enter gel phase. It’s also easier to avoid full gel phase if you’re using relatively small moulds because there is less heat build-up in small moulds than in large moulds. So, if you started your soaping with small batches in small moulds that you didn’t insulate and the progressed to larger batches in larger moulds that you insulate or oven process you may well see a progression from no rivers to rivers even if you now discount water. ‘Water discount’ is not an exact term: many regard anything less than 2.5:1 water:lye as a discount, whereas anything over a 1:1 water:lye is in fact a surplus. There’s a lot of playroom in between.
Liz
Very beautiful experiment!
Karen Harvey
Fascinating! I happen to love the crackly, glyerin river look. I have noticed this in plain soap too. You just have to look harder to see in plain soap. Thanks for sharing!
Kenna
I don’t think water plays as large of a part as most people think. I’ve commonly had rivers in soaps made with a 50% solution. The largest driving factors I’ve observed are heat and poor mixing, which I blogged about on Modern Soapmaking some time ago. Hand stirring extra water versus not hand stirring the other side is a pretty big variable that can greatly contribute to the duration of saponification and uneven speed of the chemical reaction. Interesting experiment, Clara! It would interesting to take this further and eliminate variables like additives, stirring variances, etc.
Melinda Coss
I find this really interesting. I can honestly say I have never experienced glycerine rivers in any of my soaps and that means in 20 years of soap making and an enormous variation in soap base oils. When I began making soap I used 30% water but then changed to 33%. The evidence you demonstrate is pretty conclusive but really odd that I have had such a different experience using a much higher ratio of water.
Denise Snow
Wow! Thank you for sharing this.
Maria
Well done, informative and well documented. Thank you for sharing your time and knowledge. I have a few scents I enjoy but get the dreaded glycerin rivers. Have never tried discounting the water, but I will now. Love your deco swirl tops.
Diana
Great experiment….I also noticed that I haven’t gotten them in years and that is when I started drastically reducing my water. I knew it couldn’t be the heat alone because I always go through full gel. Thank you so much for sharing your knowledge with everyone!
Ruth Esteves
Your experiment is so clear! And what a surprise that lye concentration can make such a big difference in the outcome of the soap. Thank you so much for sharing your results. You’ve really shed light on what was a soap mystery.
Jennifer
This is BRILLIANT. Love the experimental design, with all the controls. Love the results. And really love the design on top of the soap, which I’ve never seen before. Can I be you when I grow up, LOL. Thanks so much for figuring this out. Your fellow soapers thank you!
Natalia
Thanks for sharing it, Clara!So useful!
Clara
Thanks for all the valuable feedback! I’m happy if my experiment gives others food for thought and perhaps inspiration for more experiments around the rivers. My experiment was very basic and I only tested for water, ie there may be lots of other contributing factors that can be tested such as eg type & amount of pigment used, type & amount of fragrance used and fatty acid profile of the formula. More than one person has questioned my method of gradually mixing in the additional water by hand, and while the old mayonnaise chef in me is pretty confident that my emulsion was very stable (and my colourant, of course, was already carefully mixed into the oils), it’s a valid concern and so my follow-up experiment is in the oven as we speak. One thing I would like to point out is that in my experiment I kept heat constant at 60C. If you increase the heat enough you may well get rivers or streaks in low-water soap as well.
Desert Rose Handmade Soaps
Thanks for sharing, Clara. Do you think this woul apply to milk soaps?(replacing water with milk and/or half milk/half water).thanks
Clara
At 60C liquid concentration seems to be a significant factor. What you need to take into consideration is that milk contains sugar and sugar will affect the heat generated in the soap. What the practical implications of that are I don’t know; you’ll need to test it. Chances are though, that you’re more likely to see rivers in milk soaps with full liquid than in milk soaps with a big liquid discount – at an ambient temp of 60c.
Zahida
This is BRILLIANT! Great work and thanks so much for sharing! I’ve been battling glycerin rivers through my last few batches and can’t wait to whip up another batch with a water discount! THANK YOU!
Claudia Wilson
Absolutely fascinating! Thank you so much for the info.
It’s also interesting that the higher water volume soap traced slightly thicker than the lower volume water soap.
Concepcion
Very nice experiment, when you talk about the ratios, you make them in ounces or grams? example lye/water 1/2.4 that means that is 1 part lye and 2.4 parts of water? the .4 is what confuse me, unless you mean 1 oz/gms by 2.4 oz/gms?
Hope you can help me to understand this, I normally use lye/water ratio 1:2 = 1 part lye by 2 parts water.
Thanks for sharing such a great experiment, by the way love the top of your soap, how did you make the squiggles?
Clara
The ratios work in any weight unit you choose. A NaOh/H2O ratio of 1/2.4 means just like you say, 1 part NaOH by 2.4 parts H2O. If you are measuring in tons and your NaOH is 3 tons then your H2O would be 3 tons x 2.4 = 7.2 tons. That’s for a REALLY big soap! 🙂
The squiggles are made in inverted stamp technique. If you scroll through my blog posts you’ll find a tutorial about it.
Eucalypta
Interesting theory; love the test soap!
I do’t know if you noticed, but when the glycerine rivers occur with TiO2, the ends of the soap don’t display the crackles.
This is the part where the soap doesn’t gel! So heath certainly is a factor.
Accellerating FO’s tend to create glycerin rivers in a (plain or coloured) soap as well – even sometimes “geodes”. In this case less water makes the problem worse, so I fear that water reduction on its own is not the solution to avoid crackles.
IME this fenomenon occurs quite randomly. When I use oil soluble TiO2 I never experienced this problem.
(I would use a bit of water i.s.o. glycerin to mix the regular TiO2).
Clara
I’ve definitely noticed that the surface of the soap (both top, sides, bottom and ends) rarely show rivers even if the interior has lots of them. Not so sure though that that’s because these areas don’t gel. If you make an identical soap using identical method but with colour pigment instead of TD you’ll see that you have uniform deep, gelled colour all the way to the edges. Likewise, when you force gel in a relatively hot oven the soap often gels from the outside in as well as from the inside out, ie it definitely gels all the way out, yet you are more likely to see streaks inside the soap than on the surfaces. I think the lack of surface rivers has got to do with temperature differentials but not necessarily with incomplete gel.
When an fo ‘accelerates’ it increases the rate of saponification and therefore the generation of heat. If it happens in a high-water soap the soap will rapidly hit gel phase and if unlucky, overshoot typical high-water gel temp and overheat (perhaps with ‘stalagmites’ as a result). The likelyhood that a low-water soap will overshoot its typical gel temp is smaller since that temp will be higher.
I don’t think there’s much randomeness here 🙂 : it depends on temp and what exact temp that is will depend on the water concentration. How quickly the soap reaches that temp, how much it overshoots that temp or how long it stays at that temp depends on variables like mixing temps, fragrances, oils used, ambient heat, agitation etc. But if you regularly bring high-water soap with TD to full gel without ever experiencing rivers, that’s very interesting. Of course, if you add water to your colourants without discounting that water from your lye solution you increase the water content of the soap, ie you bring down the temp at which the soap will reach gel phase.
Madame Propre
What a great experiment! Thank you for all those comments, both yours and your visitors. I am learning a lot! It happened only once to me, The soap turned out even more beautiful I think. I was wandering how I could do it again! Thanks!!!
Fiona Greiffenberg
Hi Clara, Do you use an anatase or rutile grade TiO2? Best Regards,
Fiona
Clara
Sorry Fiona, I don’t know in what kind of crystal form this titanium dioxide occurred in nature or how it was treated later on. I’m based in South Africa and soap making supplies here rarely come with that kind of information.. All I can tell you is that the titanium dioxide I use is readily dispersable in both water and oil. It’s suggested that rutile might be safer but since soap is not a leave on product I’m not overly concerned with the possibility of it being anatase. My personal preference is to formulate soap with oils light in colour rather than using titanium dioxide..
Sherri Blair
Can you clarify the benefits of gelling vs. non-gelling with regards to the quality/appearance/coloring of the final product?
Clara
Gelled soap is typically more translucent than un-gelled soap. Un-gelled soap has a creamier look but colours tend to be deeper and more intense in gelled soap. After a full cure un-gelled and gelled soap may feel equally hard to the touch when dry but in use un-gelled soap absorbs water more readily than gelled soap, ie un-gelled soap becomes ‘mushy’ faster when placed in water and dissolves more readily. Everything else equal you could say that gelled soap lasts longer in use.