ResolvableOwl
Notorious Lyear
I haven't found SMF hits (prior to this thread polluting the search results) for vat-style reduced indigo as a soap colourant. This comes closest:
https://www.soapmakingforum.com/threads/indigo-pink.75897/post-794236But 1. @penelopejane didn't add (reduced) vat directly to the soap, but oxidised to indigo proper beforehand, 2. at least for now I'm less keen on pink/purple or green from indigo, but tackling a decently vibrant blue, and 3. (and most importantly) any opportunity to show off beautiful azure/denim-coloured soaps is a good opportunity!
Some of my prior efforts around indigo: (Leuco-)Indigo and a puzzling Soap Chameleon | Infusion
Step 1: Vat
I kept things conservative and stuck to the well-tried 1-2-3 fructose vat (1 part indigo, 2 parts calcium hydroxide, 3 parts fructose), just with Ca(OH)₂ replaced by NaOH (coz soap, ye know).
For random reasons I chose woad extract (66 mg). Dispersed (inside a test tube with lid) in 4.7 g of a weak 3% NaOH lye (accounting for lye in the final lye dosage). After that I added 202 mg fructose, flooded the empty space of the test tube with butane (lighter gas, poor man's oxygen-free/inert atmosphere), and closed it airtight. Upon heating and shaking, the fructose dissolves and reduces the bluish-black powder to a red-brown solution, that looks like soy sauce/iodine tincture (for now I blaming a peculiarity of woad that the colour isn't greenish-yellow as expected from vats – or is this just a matter of concentration?):
Some sediment remained undissolved, but it didn't appear dark, rather greyish, so I guess it wasn't unreacted indigo, but some other impurity.
Step 2: Soapmaking
I had made an oil blend beforehand, and added some woad extract powder (1.6% TOM to be precise) to it. Cooling down while stirring kept the powder in dispersion until it was kept there by solidifying fat crystals, no sedimentation. Let it sit for three days.
On soaping day, I made two soap batters, one from the woad-infused oils, the other from the same oils but the not infused portions. I added sorbitol at 3% TOM to the woad slurry batter, and 2.6% TOM to the vat batter (to account for the 0.4% TOM of fructose in there).
When eventually reaching light-medium trace, I opened the vat vial. The orange-brown solution started turning blue literally within seconds. I was in a hurry to pour it into the soap batter, give it a short but thorough whisk, and pour it into the mould. The batter turned into a dirty green-brown colour, with a tendency to become blue at the surface, just as I'd expect it. The effective concentration was 0.13% TOM, so less than a tenth of the “wasteful” direct infusion.
Step 3: Cutting (T+18h)
OK. Let's not talk about the soap itself, I know that I'm stupid, and my superhuman talent to provoke false trace has hit me hard this time. I'm not even sure if it made through gel phase, even though I had CPOP'd it.
I had poured the woad slurry batter first, then the vat batter, and applied a simple improvised hanger swirl design. First thing to note after unpacking: The colour depth and evenness is much better than with my previous test cubes, though I haven't put in much more indigo. Letting the indigo some time to get used to its oily environment pays off. I'm particularly glad that no bleaching at the outer sides had taken place.
Then the vat chameleon. What the actual [redacted] is going on there? The top layer is snow white. Bulk is yellowish-brown and easily discolours to a cyan blue when cut open/exposed to air, so far so good and expected. But why then is the effect strongest at the bottom, in the vicinity of the woad slurry batter? And why does it seem to be boosted by stearic spots?
But that's not all…
Step 4: Planing (T+36 h)
Over night, all that olive, green, or aqua coloured zones have become white as well. Not the faintest trace of visible indigo left
.
For several reasons, the surface needed some planing. Beneath the surface, a vibrant turquoise/azure hue appeared. Digging deeper revealed that the very inside is still at reducing conditions, i. e. yellowish and turning green within minutes when exposed to air.
Once again, the vat oxidation seems to be very picky where to happen and where not. Strongest once again close to the interface to the dark slurry zone. But the reappearance of colouration seemed to avoid the stearic-spot zones this time.
Step 5: At the sink
Thanks to the ruined oil blend/soap recipe, the soap felt quite mature already, as if it was two weeks into cure (and non-zappy), so I gave it a shot to wash my hands with it, and to erode the soap surface (the leftmost block in the upper pic).
Photographed immediately after usage; the yellow streaks have turned turquiose in the meantime (the denim blue only appears to have altered, due to lighting conditions). Just like with my (indigo carmine based) OPW soap, I'm getting the impression that there are really a lot of “surprises” hidden beneath the surface, and just wait to be rinsed away during usage!
Discussion
Under the conditions tested, indigo vat as a soap colourant has some promising/compelling sides, but is still highly unreliable. Good for surprises, at best. The bleaching on the sides is really anooying. But direct addition of reduced vat to soap batter is totally possible (though a bit of a “blind flight” since it's so hard to predict the final look).
I'm actually impressed how much colour one can get out of so little base material. I'd guess the colour depth is about half as the woad suspension, but at less than one thenth of colourant invested! It is also a smoother (no dark specks), more saturated, and brilliant colour than the slurry, though at a hue much more on the green-turquoise side.
Further directions
First and foremost I'll have to keep a close eye how these develop over time (I'll post updates here). For future trials (note to myself: use a proven and well-behaved soap recipe next time!), the concentration/proportion of vat can still be increased, I'd say threefold is very possible.
Then, I feel that the amount of fructose is very generous, since it is laid out for vat (fabric dyeing with constant air contact). Cutting down the excess of reducing agent might speed up the reappearance of the pigment and/or limit the unreliable discolouration. From naïve stoichiometry, a ratio of 1:1 (instead of 3:1 of the 1-2-3 vat recipe) might be sufficient. In the end, thanks to air-free dissolution/reduction, I don't lose any fructose to oxygen in the preparation.
On top of this, the botanical source of the indigo is a free parameter.
https://www.soapmakingforum.com/threads/indigo-pink.75897/post-794236But 1. @penelopejane didn't add (reduced) vat directly to the soap, but oxidised to indigo proper beforehand, 2. at least for now I'm less keen on pink/purple or green from indigo, but tackling a decently vibrant blue, and 3. (and most importantly) any opportunity to show off beautiful azure/denim-coloured soaps is a good opportunity!
Some of my prior efforts around indigo: (Leuco-)Indigo and a puzzling Soap Chameleon | Infusion
Step 1: Vat
I kept things conservative and stuck to the well-tried 1-2-3 fructose vat (1 part indigo, 2 parts calcium hydroxide, 3 parts fructose), just with Ca(OH)₂ replaced by NaOH (coz soap, ye know).
For random reasons I chose woad extract (66 mg). Dispersed (inside a test tube with lid) in 4.7 g of a weak 3% NaOH lye (accounting for lye in the final lye dosage). After that I added 202 mg fructose, flooded the empty space of the test tube with butane (lighter gas, poor man's oxygen-free/inert atmosphere), and closed it airtight. Upon heating and shaking, the fructose dissolves and reduces the bluish-black powder to a red-brown solution, that looks like soy sauce/iodine tincture (for now I blaming a peculiarity of woad that the colour isn't greenish-yellow as expected from vats – or is this just a matter of concentration?):
Some sediment remained undissolved, but it didn't appear dark, rather greyish, so I guess it wasn't unreacted indigo, but some other impurity.
Step 2: Soapmaking
I had made an oil blend beforehand, and added some woad extract powder (1.6% TOM to be precise) to it. Cooling down while stirring kept the powder in dispersion until it was kept there by solidifying fat crystals, no sedimentation. Let it sit for three days.
On soaping day, I made two soap batters, one from the woad-infused oils, the other from the same oils but the not infused portions. I added sorbitol at 3% TOM to the woad slurry batter, and 2.6% TOM to the vat batter (to account for the 0.4% TOM of fructose in there).
When eventually reaching light-medium trace, I opened the vat vial. The orange-brown solution started turning blue literally within seconds. I was in a hurry to pour it into the soap batter, give it a short but thorough whisk, and pour it into the mould. The batter turned into a dirty green-brown colour, with a tendency to become blue at the surface, just as I'd expect it. The effective concentration was 0.13% TOM, so less than a tenth of the “wasteful” direct infusion.
Step 3: Cutting (T+18h)
OK. Let's not talk about the soap itself, I know that I'm stupid, and my superhuman talent to provoke false trace has hit me hard this time. I'm not even sure if it made through gel phase, even though I had CPOP'd it.
I had poured the woad slurry batter first, then the vat batter, and applied a simple improvised hanger swirl design. First thing to note after unpacking: The colour depth and evenness is much better than with my previous test cubes, though I haven't put in much more indigo. Letting the indigo some time to get used to its oily environment pays off. I'm particularly glad that no bleaching at the outer sides had taken place.
Then the vat chameleon. What the actual [redacted] is going on there? The top layer is snow white. Bulk is yellowish-brown and easily discolours to a cyan blue when cut open/exposed to air, so far so good and expected. But why then is the effect strongest at the bottom, in the vicinity of the woad slurry batter? And why does it seem to be boosted by stearic spots?
But that's not all…
Step 4: Planing (T+36 h)
Over night, all that olive, green, or aqua coloured zones have become white as well. Not the faintest trace of visible indigo left
.For several reasons, the surface needed some planing. Beneath the surface, a vibrant turquoise/azure hue appeared. Digging deeper revealed that the very inside is still at reducing conditions, i. e. yellowish and turning green within minutes when exposed to air.
Once again, the vat oxidation seems to be very picky where to happen and where not. Strongest once again close to the interface to the dark slurry zone. But the reappearance of colouration seemed to avoid the stearic-spot zones this time.
Step 5: At the sink
Thanks to the ruined oil blend/soap recipe, the soap felt quite mature already, as if it was two weeks into cure (and non-zappy), so I gave it a shot to wash my hands with it, and to erode the soap surface (the leftmost block in the upper pic).
Photographed immediately after usage; the yellow streaks have turned turquiose in the meantime (the denim blue only appears to have altered, due to lighting conditions). Just like with my (indigo carmine based) OPW soap, I'm getting the impression that there are really a lot of “surprises” hidden beneath the surface, and just wait to be rinsed away during usage!
Discussion
Under the conditions tested, indigo vat as a soap colourant has some promising/compelling sides, but is still highly unreliable. Good for surprises, at best. The bleaching on the sides is really anooying. But direct addition of reduced vat to soap batter is totally possible (though a bit of a “blind flight” since it's so hard to predict the final look).
I'm actually impressed how much colour one can get out of so little base material. I'd guess the colour depth is about half as the woad suspension, but at less than one thenth of colourant invested! It is also a smoother (no dark specks), more saturated, and brilliant colour than the slurry, though at a hue much more on the green-turquoise side.
Further directions
First and foremost I'll have to keep a close eye how these develop over time (I'll post updates here). For future trials (note to myself: use a proven and well-behaved soap recipe next time!), the concentration/proportion of vat can still be increased, I'd say threefold is very possible.
Then, I feel that the amount of fructose is very generous, since it is laid out for vat (fabric dyeing with constant air contact). Cutting down the excess of reducing agent might speed up the reappearance of the pigment and/or limit the unreliable discolouration. From naïve stoichiometry, a ratio of 1:1 (instead of 3:1 of the 1-2-3 vat recipe) might be sufficient. In the end, thanks to air-free dissolution/reduction, I don't lose any fructose to oxygen in the preparation.
On top of this, the botanical source of the indigo is a free parameter.
your experiments
