Infusion

[Tara_H]

I've used this method to reduce my indigo and it certainly makes the indigo powder go further.

Ah, very interesting, thanks! I'd never heard of reducing it with lye but that makes a lot of sense. From that point of view I would expect that adding the indigo to the lye water before mixing with the oils would give the best result, so that all the indigo is fully reduced and green before creating the soap. That would allow it to bind fully to the soap batter as it oxidises rather than sitting alongside, which I would imagine would give a better and more lasting colour?

That might be one reason people dying fabric bother to do it.

For dyeing fabric, if you don't do this it just won't work, it'll basically wash off the first time you wash the clothes. It has to be reduced in order to bind to the fibres.

 

[Mobjack Bay]

@Tara_H I use the indigo in lye method occasionally (see the photos linked in post #6). It works well, especially if you want to make a batch of indigo colored soap and know how much indigo you want to add to achieve a desired shade. There’s a lot more discussion about using indigo and many photos in the thread I linked in post #6.

NaOH is a stronger base than ammonia and creates the high pH conditions that are necessary to “wet” or possibly dissolve indigo pigment, but I haven’t seen any visual evidence that indigo changes to the “white” water soluble reduced form when I make soap. Whether added with oil or to the lye, it stays blue, or grey, which makes me think the plant indigo is not going through the reduction process that happens in a dyer’s vat. Maybe I’m relying on very fine particles of indigo in the oxidized form to color my soap. If I let a jar of plant indigo powder + oil sit undisturbed for a long time (weeks), the blue color settles to the bottom and the oil in the jar stays pink. I have used the pink oil to make pale pink soap. The color holds up well (> 1 yr) in soap.

 

[KimW]

I love this thread!!!

 

[Tara_H]

(see the photos linked in post #6)

Ah, thanks for drawing my attention to the link, I had skipped over it on the original reading! You have some truly beautiful soaps in that thread

The impression I get, looking over all the various posts, is that the soaps where you had previously treated the indigo with ammonia give a much more vivid and lasting blue than the ones where it's prepared differently. Would you say that's a correct interpretation of the pictures? It would back up my experience in wool dyeing that ammonia is the way to prep indigo, but I don't know why it would make so much of a difference over the lye alone.

I don't have any indigo or similar at the moment so it's all academic for me right now, but I've been planning on growing woad, which I believe is prepped the same way for dyeing, so I'm interested in gathering more background knowledge on all of this! I guess I have some more research to do yet.

 

[Ladka]

Ah, very interesting, thanks! I'd never heard of reducing it with lye but that makes a lot of sense. ...

For dyeing fabric, if you don't do this it just won't work, it'll basically wash off the first time you wash the clothes. It has to be reduced in order to bind to the fibres.

Indigo is not reduced with lye, it is reduced by a reducing agent (like Thiourea Dioxide or Sodium Hydrosulfite) in an alkaline solution (provided by lye).

 

[Mobjack Bay]

Ah, thanks for drawing my attention to the link, I had skipped over it on the original reading! You have some truly beautiful soaps in that thread

The impression I get, looking over all the various posts, is that the soaps where you had previously treated the indigo with ammonia give a much more vivid and lasting blue than the ones where it's prepared differently. Would you say that's a correct interpretation of the pictures? It would back up my experience in wool dyeing that ammonia is the way to prep indigo, but I don't know why it would make so much of a difference over the lye alone.

I don't have any indigo or similar at the moment so it's all academic for me right now, but I've been planning on growing woad, which I believe is prepped the same way for dyeing, so I'm interested in gathering more background knowledge on all of this! I guess I have some more research to do yet.

When I made the soaps with the indigo in ammonia, I think I was using Jacquard brand “pre-reduced” synthetic indigo. It‘s pure indigo pigment and very strong. I think Nurture says their natural plant indigo powder is 7 or 8% indigo pigment, compared with 100% in the synthetic version. The synthetic version also won’t have any impurities, which might impact color. I can’t be sure about fading unless I go back and check soaps and methods.

 

[penelopejane]

Ah, very interesting, thanks! I'd never heard of reducing it with lye but that makes a lot of sense. From that point of view I would expect that adding the indigo to the lye water before mixing with the oils would give the best result, so that all the indigo is fully reduced and green before creating the soap. That would allow it to bind fully to the soap batter as it oxidises rather than sitting alongside, which I would imagine would give a better and more lasting colour?


For dyeing fabric, if you don't do this it just won't work, it'll basically wash off the first time you wash the clothes. It has to be reduced in order to bind to the fibres.

Adding it to lye does mean you can use a little less than just making a slurry with the powder. But, following the directions on the link I gave before and using Thiourea Dioxide and aerating it (I use a fish tank aerator pump for 30 mins) turns the indigo green. The oxydised indigo goes a lot further - you use a lot less. I’ve never tried ammonia so it might be the same.
The pre reduced synthetic indigo is just a chemical dye. Great if you don’t want A natural product. See the link I gave before. You can get a lovely pale green to deep teal blue.

 

[ResolvableOwl]

I'm a bit late to the party; I don't know how I could overlook this thread in the first place.

Indigo is not soluble in oil, to start with.

Yes and no. It's actually a bit more complicated. Most often, when indigo is used as a blue soap pigment, its solubility in oil indeed doesn't play a role, it's applied as a more or less thick slurry, and the colouration comes from indigo particles in suspension, not true solution. In this sense, indigo indeed is insoluble for the practical purposes of using it as a blue pigment, and the designation “infusion” is somewhat misleading, better call it “slurry”.

However, the coloured molecules in indigo in fact are sparingly soluble in oils (better in hotter oils), and give a purplish-pink solution (true, clear solution, not just a suspension).

This is much closer to a true “infusion” than what is commonly referred to as “indigo infused oil”. Due to the low concentration, it is not a particularly intense colourant, but that doesn't keep people from tinting soap in pink shades with it.
Besides this, indigo is also a bit soluble in pure (100% water-free) acetic acid, to give a rust-brown solution:

Hence I wonder if glacial acetic acid might be of use as a solubiliser of indigo into oils? Just upping the NaOH accordingly would just give sodium acetate in the final soap, which is a useful compund on itself.

 

[Mobjack Bay]

There’s also a long thread on indigo pink. I didn’t post a photo until very late in the thread. The last time I looked, which would have been around the 18 month mark, the soap was still pink. I’ve also had light blue indigo soap turn purplish pink and then pink over time.

 

[ResolvableOwl]

Hehe, yes. I found that thread too. Very informative everything! Though @penelopejane's vat-in-soap idea hasn't addressed there yet. That's one thing I'm tackling atm. .

 

[ResolvableOwl]

Tiny update: Indigo-infused canola wax. You have to see it to believe it. Yes, that's the very same wax on the left and the right! And the molten wax will turn blue again when solidified.

 

[ResolvableOwl]

Though @penelopejane's vat-in-soap idea hasn't addressed there yet. That's one thing I'm tackling atm. .

https://www.soapmakingforum.com/threads/indigo-vat-as-soap-colourant.84739/