All things Chiba and Dichromate alternatives.

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I had the day off today, so I spent some time experimenting with carrageenan and reading about the success of the fish glue Chiba process. That got me thinking it might be worth starting a post dedicated entirely to Chiba methods. There’s a lot to explore, especially about avoiding dichromates and finding alternative materials that respond to other sensitizers. I had AI format this to make it more readable, I am an engineer and a horrible writer.

Here’s a list of materials I’ve tried that can form images in a gum-like process. For all of these, I’ve used safe sensitizers such as ferric ammonium citrate and ferric ammonium oxalate.
PVA SBQ seems to behave most like gum. SBQ is pricey, but you don’t need much of it, and it’s not carcinogenic. The SBQ process is chemically different from Chiba, though.

Processes that need thermal control during hydrogen peroxide development​

• Fish glue – Has produced some impressive images. I haven't tried it
• Rabbit glue
• Gelatin – Your house will smell like dead animal and you'll have this hint of dead animal with you at work if you don't use gloves. I love jello and I expected so much better.
• CMC (carboxymethyl cellulose) – Must stay above 20 °C at all times per Habib Saidane, which is easy in warm climates but tricky here in Washington State for most of the year.
• Iota carrageenan + gelatin – Worked when mixed and exposed in cold as well as warm water. Several papers suggest that lambda and kappa carrageenans also respond to UV with Fe³⁺ salt

Processes that develop at room temperature (near 20–25 °C)​

• PVA – Works well, you add citric acid and keep the temperature below 40 °C. Produces consistent images, though tonal range is limited. Cyanotype also develops nicely in it.
• PVA + CMC – Same as above: add citric acid and stay below 40 °C or all of it will harden and you'll get no image.
• PVA + Sodium Benzoate and citric acid forms a white precipitate gel that is great for mixing and paintting using a brush. Cyanotype also develops nicely in it.
• PVA + dilute boric acid – This follows the classic slime formula. A 10–20% boric acid solution in water works; higher concentrations cause precipitation.
• Iota carrageenan + gelatin – Works when mixed and exposed in cold or warm water.
• PVA mixed into carrageenan gelatin – Foams heavily and the foam doesn’t dissipate quickly (or ever). I lack the patience for that, but once dry it does form an image.

Things that don’t work​

• Ferric ammonium oxalate + gelatin, causes problems such as separating from the pigment.
• Heating PVA+Citric acid crosslinks PVA so you can't try it with a heat gun or develop it in hot water.
• Developing in water only. My water is alkaline and usually just washes off images on command.
• Gelatin and PVA don’t mix well, also separate from the pigment.
• PVA + CMC doesn’t hold pigments in suspension. The pigments settle in the pits of cold press paper after a few minutes. But it is good as a sizing because it doesn't dissolve very easily.

I recently found a great paper source: the Prudiut Store on Amazon sells 300-sheet packs of A4 300 GSM 100% cotton paper for about $58. It doesn’t need acidification for cyanotype or Chiba. It just works. They ship cheaply, so expect some corner damage (mine arrived fine, though). The box even came with a bonus bag of air, which I found amusing. like the packer thought, “You look like you could use this balloon!”

For all these processes, you need to size your paper and apply a clear coat after each layer. Otherwise, the layer underneath can re-dissolve. I use the same PVA or PVA–CMC mix for both sizing and overcoating. These aren’t sensitized; just let them dry and apply the next layer quickly. Be gentle during washing, too much agitation will destroy the image. I’ve found it best to lay the paper face-down in water after peroxide treatment and leave it still. PVA, once hardened properly, can take ages to dissolve, so you can rinse it with hot water or even under the faucet without damage. The resulting image has a rubbery feel wet and a chalky mat feel when dry. You can even spray with boric acid after development and heat it to lock the image more permanently.

Other notes​

• At 365 nm and lower wavelengths, sodium benzoate works as a photoinitiator. At longer wavelengths, it doesn’t do much.
• Ammonium persulfate behaves similarly and has some effects that I have not explored yet. Its supposed to develop the image as it is exposed, needing only water afterwards but that was not the case when I tried.
• I also tried a TEOA + riboflavin dye mix with little success.
• You can mix any of the gels above with small amounts of clear water-based 3D printer resin and get an image, but I wouldn’t recommend it. The chemicals are carcinogenic, which defeats the purpose of finding safer alternatives to dichromates. Additionally they smell.

Pigments tested​

• Failures:
• Poster paint (chalk-containing types fail completely)
• Acrylic paint (no luck)
• Successes:
• Graphite powder – very gritty
• India ink – stains paper if unsized
• Mica powders – including fluorescent ones (they fog exposure a bit, but look beautiful under UV)
• Watercolors – best overall results

Always use proper PPE and wear orange or red safety glasses! Studies show blue light is most associated with cataract formation, and UV will damage your eyes too. I tested with 365 nm UV lamps, and with 385nm using a UV projector. For negative exposures printed on inkjet transparency, anything between 365 nm and 400 nm should work. I’ve tried 395 nm and even blue light both are slower, but effective. For projection setups, 385 nm is the sweet spot since it penetrates better than 365 nm while staying within a useful range. My current setup uses a 50 W 385 nm LED (about 10 mm square), and it handles the job nicely.

Overall, this mix of safer sensitizers and alternative binders has opened up a lot of room for experimentation. The Chiba-inspired processes might not replace dichromate-based gum completely, but they’re getting close—and they’re much safer to work with. If anything this has become a passtime with no end in sight. I could probably continue experimenting until my grand kids pry my arthritic body parts off my chemical bottles. I got no grandkids yet.