Pigment printing processes: Gum bichromate vs Bromoil vs Oil vs Gumoil

Hi! I am very interested to try one of these processes. I have been reading about them but I would like to ask experimented users how they compare these processes one to another (objectively and subjectively). I know some of the basic technical differences (for exemple Bromoil can be used with an enlarger, etc.) but would like to know from people who tried some or all of these processes. How does the end result compare? I like the painterly effect that all these processes seem to be able to achieve. When browsing through Flickr it's sometimes difficult to feel the difference in the end result between those processes. It also seems possible to achieve polychromatic prints with all of them. Gumoil gives me the impression of giving less control than bromoil during the process and even less so than oil...
Also I like the idea of being able to combine with another process. Is gum bichromate the only process among these that allows such things?
All inputs appreciated.
Thanks!

Out of gumoil, bromoil, and gum bichromate, I prefer the look of gum bichromate. But the king of pigment printing for me is carbon transfer.

The other thing to keep in mind is that Gum is an "additive" process, in that the image can built up by layers of pigmented gum. The others are "reductive", in that you are removing pigment to reveal your image... this is part of what gives the images their "look".

When I began experimenting with alternative photographic processes I started doing gum bichromate prints because of the pictorial look, it is inexpensive and you can use a great variety of papers. Most people do gum printing with layers of different colors but I only did monochrome prints with layers of the same color (black). All of these processes use bichromates in gum arabic as the sensitizer which hardens selectively according to the amount of light received and mainly differ in their binding material and the pigments. In bromoil, a gelatin silver bromide is bleached and the silver is replaced with ink. Gumoil is a positive transparent image that is contact printed to an unpigmented gum arabic surface that has been sensitized with potassium bichromate (see link below to Anna Ostanina's site, she also has a number of youtube videos demonstrating the process)

The main caveat of these processes is the use of bichromates (dichromates) and that is the reason I don't do gum printing anymore. It is a nasty chemical, it has been banned in the EU and it should be banned everywhere. If you go that path, you should collect the gum-developing run off into a plastic tank, convert it to trivalent adding sodium thiosulfate (spent fixer). It is now trivalent chromium compound that is much safer but you can go further and make it safer for disposal with more treatment. And by disposal I mean taking it to a hazardous waste disposal center. Be aware that some pigments are also toxic. You need to wear a particulate respirator and if you don't have one it could be difficult to get now because of Covid.

It seems that there is an alternative to dichromates using something called "Diazo sensitizer" but I didn't try it.

https://www.alternativephotography.com/gum-diazo-printing-v1-4/

There is also a photographer/printer who claims to have a safe alternative to dichromates. She calls it "ecoGumoil".

https://annaostanina.com/ecogumoil


There are a couple of books that go over pigmented processes:

https://www.amazon.com/Photographic...tographic+possibilities&qid=1619973758&sr=8-2

https://www.amazon.com/Dimensions-P...sion+in+photo+processes&qid=1619973784&sr=8-1

aldus_manutius said:

The other thing to keep in mind is that Gum is an "additive" process, in that the image can built up by layers of pigmented gum. The others are "reductive", in that you are removing pigment to reveal your image... this is part of what gives the images their "look".

Click to expand...

Are you talking about full colour or monochromatic gum? Pigment is also removed for monochromatic gum. For more density, layers of pigment are added.

Andrew O'Neill said:

Are you talking about full colour or monochromatic gum? Pigment is also removed for monochromatic gum. For more density, layers of pigment are added.

Click to expand...

I was specifically referring to polychrome and yes, density can be increased by “adding” pigment (hence my comment about being an essentially additive process. Of course one can always go “wild and crazy” on the image and work it any way one wishes (the beauty of alt/proc photography).