Pigments

[bob carnie]

Hello All

Bmikten started a thread about where our work should end up and I and a few others hijacked it and turned the discussion about pigments , which I apologize for.
I would like to talk about pigments, not dyes, and how people work with them ways of staining wood, ways of printing with them, ideas on how to crush stone and make to paste, basically
use this thread to gain more information about them.


I will start it here with a post by Drew W.

That technique is called "ebonizing". But there are much safer and less expensive formulas than the dichromate route, easily searched on the web. The wood itself needs a high tannic acid content. So some wood species darken far more than others. But using such a solution also raises the grain, so you have to polish or fine sand everything down again afterward, prior to a final sealant. A major wholesale frame factory in this area had a lot of demand for that, with one employee dedicated to it almost full time. But due to the substantial extra cost of the appropriate hardwoods, as well as extra labor expense, they eventually switched entirely to Black Cat ink for their opaque black wooden frames. However, a partial chemical ebonizing might simulate ammonia fuming of white oak without the awful health risk involved with that.

Now as per that linked insane "death wish" toxic voodoo method of enhancing cherry ... escape the Medieval Inquisition torture chamber and acquire a modern transoxide colored sealant. I've used something called Cetol 1 for both personal picture framing and cabinetry needs, as well as massive architectural restorations (including one entire Frank Lloyd house, inside and out, plus furniture - a six million dollar renovation project). It's totally lightfast, truly transparent, penetrates deeply, and is dispersed in oil sealant, so allow it to thoroughly outgas before putting artwork in the frame. There is also a water-based equivalent, but it's not as deluxe to apply.

And yeah, it might be nice to section all this off to a separate thread.

[Drew Wiley]

OK - to supplement that, the most advanced pigment research naturally applies to where there is the most financial incentive - auto paints, and namely, where a deep translucent or transparent "3D"look is desired instead of an opaque one. Transoxides can be made in almost nano scale, so tiny as to be transparent, so might be of interest in alt photo applications. The down side is that, being oxides, no reasonable process set is possible. You could achieve an off-color image, kinda like an exaggerated version of Godfather movie filtering, or some other fun effect. And I don't know if some of these might "poison" gelatin and cause carbon or carbro gelatin to prematurely cross-link and embrittle. But in terms of wood finishes, this category of commercial pigments offers all kinds of opportunities.

In terms of industrially available pigments of well-tested lightfastness and high batch to batch consistency, the finest ground are probably Genex. And in that case, a true non-toxic process set is feasible.

Rockhound style mineral hunting can be fun. My dad was into that, and would take me out of school for weeks at a time, touring the deserts and mountains. I learned more from him anyway. I once took a bizarre shot in Utah of bright blue gopher mounds atop a red clay alluvial wash, due to them burrowing into a different layer below. All kinds of interesting agates and calcites were laying around too. In that general area, there are places where different colored sandstones layers are each only several inches thick, and are sometimes exposed adjacently : purples, turquoises, deep blues, reddish tones. Some interesting days packing in big cameras, that's for sure.

A pal of mine up the hill built their own house using trucked in Moenkopi red sandstone, Brazilian granite, and personally milled cherrywood cabinetry. I supplied them with the specialty transoxide finishes, which could be layered up to an excellent match. But he wanted unique cabinet knobs, so as an outdoorsmen himself, explored creek beds in the desert of Baja California, and came back with reddish "desert varnished" pebbles which matched his woodwork, and could be epoxied onto his cabinet doors and drawers using metal stems hidden behind. The coolest part of the project was their master bathroom. He took a color panoramic photo of the east side of the crest of Sierra at sunset, then replicated that using overlapping various shades of marble, broken or otherwise shaped to match the scene.

I've been involved with many many analogous projects. In fact, the same chemical supplier which catered to the local pharmaceutical industries supplemented their business not only selling darkroom chemicals, but all kinds of coloring substances coveted by metal platers, potters, stained glass craftsmen, and classic faux finishers. No longer in business due to a premature family death. But everyone who worked there, even at the sales counter, had a phD, so had serious knowledge of their products. At a more down to earth level, the thick venerable The Artists Handbook, which has gone through many revisions, is an excellent introduction to artist pigments per se.

[bob carnie]

Thanks Drew, though rockhound style mineral hunting is not what I intend to do I actually have some friends and clients that may be willing to do a bit of this. I really like the idea of getting down to the key basics, the post in the other thread blew my mind about potassium dichromate as a vehicle for staining cherry wood for example, I have been trying to understand the relationship between Gum(tree sap) Ammonium Dichromate and UV light and in this one post I saw the link to how it all works.
I do not come from a well educated background, but rather school of hard knocks so I love this learning experience later in life and when I can put two and two together to equal four, well is very satisfying.

[koraks]

I'll follow this thread with interest! I don't have much to contribute as I have only an elementary knowledge of pigments as it stands, but they've always fascinated me.

I do have a probably easy question concerning pigments for B&W carbon transfer. I'm looking for a good neutral to cool black pigment, preferably already dispersed, so something like watercolor paint or whathaveyou.

So far I've been using Talens India ink and acrylic paint. The India ink works very well and is technically superior to the acrylic, which seems to have some additives in it that create a very, very faint oily veil on the tissue, and it also shows up on pure whites very faintly. Otherwise it prints OK, that is at least lamp black. I've also tried oxide black (essentially iron oxide) and it's more problematic; it seems the dispersion isn't nearly as good as that of the lamp black paint and the India ink. It doesn't seem to create very big problems in the print and the print tone appears to be perfectly neutral, but I expect the tendency of the pigment to coagulate and/or the variations in particle size will at some point result in problems in the highlights.

I'm located in Europe so not all products may be available to me. Worst case scenario I'm prepared to make my pigment dispersions at home, but I'm painfully aware of the complexities of doing so, hence my preference at this point for an already dispersed form.

PS: I can of course add colored pigments to lamp black to shift the tone, and if there's really no other option I'll keep doing this, but I want to explore the possibilities of a truly neutral pigment.

PPS: The Wet Print (based in Spain) I know sells a very nice pigment, but (1) it's lamp black so warm-toned, and (2) they recommend the very ink I had already been using for carbon transfer.

PPPS: I'm aware of the existence of other varieties of essentially burned stuff; i.e. vine/vineyard black, ivory black etc., and while some are a tad more neutral than lamp black, they're all distinctly warm-tone.

[Drew Wiley]

Lamp black is inherently purplish, and mineral blacks are distinctly greenish. I have a lot of background in industrial pigments, and state this simply to hint that a paint store is not a good place to look for a photographic black. Pigment dispersion can itself be a complex science. With watercolor pigments, acrylics, etc you have to be careful no added preservatives like formaldehyde are present which can "poison" the gelatin. Sandy King once hosted a Carbon Printing forum which discussed a lot of this kind of thing.

[koraks]

Thanks Drew, yes, I'm aware of these challenges. Btw, the iron oxide black I tried is neutral enough; if there's a greenish hue to it, it's sufficiently subtle not to be objectionable. Other than that, I agree that the local arts supply store may not offer the best solution. They have a wide range of pigments, 7 or do of them are black, but none of them qualifies. As to the paints they stock, the selection is naturally narrower.
India inks btw are also a mixed bag; I trialed those when I first started out with carbon printing and found that several were combinations of a black pigment and dyes to shift the color in the desired direction. All of these dyes stained the paper badly, of course.

[Drew Wiley]

There are so many kinds of inks too. Fortunately, some very skilled carbon printers participate in this forum and can probably answer your questions about that aspect. I have sometimes worked with inks in relation to woodworking; but that's something quite different. I never got past certain process color experiments in carbon, since I planned to dedicate the time to learning dye transfer printing instead, which is capable of great depth of black without resorting to a K printer. But alas, even that has fallen through, schedule-wise, once I got into making high quality internegs suitable for advanced levels of chromogenic printing. Maybe in another lifetime.

[Vaughn]

For a neutral black in my carbon prints (single transfer) I have found the watercolor lampblack in tubes to be excellent. I have been using Grahams...but that is a west coast USA company and probably not available across the sea. I started off using Grumbachers Academy grade lampblack. No issues.

The pigments of watercolors in tubes is finely ground, well dispersed, consistent, and easily to measure and use. A little more $ than doing everything yourself, but the cost is a minor expense when taking in everything else. Also depends on one's volume of work produced, of course.

I often add a little Burnt sienna or similar for a little warmth.

[koraks]

Thanks for chiming in Vaughn. I'll have a look at the watercolor selection down at the shop next time when I visit town; probably next week to pick up some prints they're framing for me. I wonder if the lamp black in Graham's is cooler in tone than what I get from the acrylic paint I'm using. Btw, the acrylic lamp black is already considerably more neutral than Talens India ink, but still distinctly warm.

You're certainly right about the chore of making a good dispersion vs. getting one that's pretty much ready to go. Cost savings aren't my motive; it's just that so far it seems hard to find a finished product that offers the tone that I'm looking for.

@Drew, yes, color carbon...that's something else. I know I would have to go through digital negatives to get that to work, realistically. And that's a rabbit hole I'd prefer to avoid for now, if I can. Maybe, one day. For now I'd just like to become proficient enough in B&W carbon so that I can fairly reliably select the right tissue, sensitizer concentration and exposure time based on any given negative I make. I'm right now looking at a 4x5" carbon transfer onto glass that I made this morning; it has a few imperfections, but it has that unique quality that no other printing process seems to offer.

[Vaughn]

I tried a French brand of lampblack watercolor (starts with an "S") that was very warm -- closer to what I have found with Ivory black. So there seems to be a variation in what lampblack actually is.

Some folks will add a little blue of some type to counter any warmth. I find Black Cat to be too warm (and glossy) on its own for me. But I have used Sumi ink in the past -- on its own (very warm, of course) but also to mix with lampblack to add a little warmth.

[bob carnie]

I am going to do a workshop with my staff in the fall with The Pigment Hunter, first on our list is to be able to make the pigments we use daily for our gum prints . Then we may expand this workshop to explore Earth Pigments and techniques of grinding down to our specs, We use a lot of them here and also we can expand to staining our woods for framing which would be a secondary wormhole to go down.

Right now it CMY and a good Sepia that we are currently using is what we are tying to achieve with this workshop.

[Drew Wiley]

It's hell just finding a true black enamel. They might look black full strength, but betray something else if toned down a bit. One of the best came from Holland, and was especially expensive, but of no use in the context here because of the solvents and oil vehicle involved. But I mention this simply due to the fact that several different black pigments need to be combined to achieve a neutral result. Given the fact that some artist's pigments cost far more per volume, those manufacturers have more incentive to carefully combine ingredients.

[Ron McElroy]

I tried a French brand of lampblack watercolor (starts with an "S") that was very warm -- closer to what I have found with Ivory black. So there seems to be a variation in what lampblack actually is.

Some folks will add a little blue of some type to counter any warmth. I find Black Cat to be too warm (and glossy) on its own for me. But I have used Sumi ink in the past -- on its own (very warm, of course) but also to mix with lampblack to add a little warmth.

Sennelier?

[bob carnie]

It's hell just finding a true black enamel. They might look black full strength, but betray something else if toned down a bit. One of the best came from Holland, and was especially expensive, but of no use in the context here because of the solvents and oil vehicle involved. But I mention this simply due to the fact that several different black pigments need to be combined to achieve a neutral result. Given the fact that some artist's pigments cost far more per volume, those manufacturers have more incentive to carefully combine ingredients.

I have been mixing together c, m, y in equal amounts and get a very nice dark grey, I think finding a good black for gum printing is difficult, we will do a lot of testing on this, if you use the black as the first layer in the types of prints I make you can use a opaque pigment which opens the door for various possible pigments to use.

[Drew Wiley]

Yeah, gum is somewhat different. You'll probably need some kind of K printer opaque black for certain images, and it might need to be a blend. Wish I had an answer; but in my pigment background I had a relevant saying : there is never any such thing as pure white; nor is there any such thing as real black. The eye has to be fooled into thinking it so via sheer saturation, or by offsetting one hue bias with another. Black is the Achilles heel of inkjet printing.

[koraks]

I do have a probably easy question concerning pigments for B&W carbon transfer. I'm looking for a good neutral to cool black pigment, preferably already dispersed, so something like watercolor paint or whathaveyou.

To answer my own question: it turns out that Kremer Furnace Black Pbk7 (which is essentially the same as 'lamp black' AFAIK) is a very neutral pigment of a fine grind and high tinting strength: https://www.kremer-pigmente.com/en/shop/pigments/47250-furnace-
black.html
It's a powdered pigment so needs to be dispersed, but since posting my question back then I got into using dried pigments and have figured out (I think) how to make a decent quality dispersion, provided the pigment is of good quality, esp. uniform and small particle size.
I have yet to try Kremer's XSL black, which is essentially the same pigment, but bound to a vehicle that should make it easy to disperse by simply stirring the tiny pellets in water. https://www.kremer-pigmente.com/en/shop/pigments/xsl-pigments/26600-xsl-black.html


Here's a quick 4x5 I made with the Kremer Pbk7. The tissue is a 0.25% Pbk7 and 8% gelatin (so ca. 0.31g pigment per 10g gelatin), which already gives a rather high contrast. I think a more reasonable loading would be around 0.1g pigment per 10g gelatin.
https://tinker.koraks.nl/wp-content/uploads/2022/11/20221112_1129361.jpg

[bob carnie]

I am interested in the permanence values of pigment that I use, Right now I am using The Wet Print and Daniel Smith.. The wet print pigments are rated Blue Wool Scale of 8 - which is suppose to be pretty good, I am not sure what the BWS rating is for Daniel Smith. they just say on the packaging High Permanence, transparent, low stain, and low granularity, It took me a long time looking at all their charts to come up with a good set of tri colour pigments, I had to mix equal Green and Blue to get my cyan to be of the same qualities of the yellow and magenta.

We as photographers are a funny breed where some of us are obsessed to colour permanence, I think in part a lot of us are old enough to remember the pain of fading C prints (dye coupler).. This obsession with permanence does not seem to be the case with painters.
I am wondering if some of you have links to references of the relative merits of different pigments . Permanence Levels - Opacity to Transmission Levels- Staining Levels and of course Granularity.

Right now I am stuck at Blue Wool Scale - and wondering if anyone has gone further down this wormhole....

Drew I do know you invented photography in the High Sierras with Bigfoot in the caves where you ground pigments together, it amazes me that Nicephore Niepce visited you in the 1800's and even more that you are actually that old but I am looking for some real world info that can lead me to the right answers to my needs.

thanks in advance.

[koraks]

Bob, the best I can offer is something you probably already know about; the excellent overview of pigments compiled by Bruce MacEvoy at handprint.com; follow this one for the pigment index: https://www.handprint.com/HP/WCL/palette1.html It's conveniently grouped by color and within that on pigment code. You'll find the pigments in your Daniel Smith paint listed on the tube. He lists blue-wool scale ratings (not sure what source is he used) combined with his own testing (which he has done for a surprising number of pigments).

There's also this very comprehensive and easily accessible pigment database: http://www.artiscreation.com/Color_index_names.html
It consists of information compiled from several sources, including handprint.com, so to an extent it's redundant - but more comprehensive as it lists some pigments that handprint.com doesn't.

However, when it comes to permanence, I fear that figuring out how well your pigments will fare is a tricky proposition at best. The ratings provided by manufacturers or independent parties will give an indication, but if I look at the inconsistenties in some cases between for instance MacEvoy's findings and the industry-supplied ratings, it's clear that there are many nuances. Then there's the issue that a pigment of the same code (let's say PR122 or PB15:3) can differ between manufacturers, and as a consumer you never know what kind of differences there are - or even where the pigment you're using actually comes from. Relevant differences might be particle size or subtle chemical differences/impurities that can have an impact on the chemical stability of the pigment.

To make matters worse, sometimes, characteristics can be a blessing and a curse at the same time. For instance smaller particle size will generally result in higher tinting strength and higher chroma, but will also make the pigment more sensitive to chemical attack and hence fading, darkening or chroma loss.

I can imagine that further complications come from the way the pigment is used; there can be advantages (a matrix like gum or gelatin might protect the pigment locked inside of it) or disadvantages (traces of dichromate or other chemicals may form a threat to long-term stability). Long story short; it seems that the advice given by people like MacEvoy to do your own testing is probably not just a luxury, but an actual necessity if you want to determine if the pigments you, specifically, are using are sufficiently lightfast. I don't take it that far and just hope for the best based on the data I can find online.

That the lightfastness issue is hairy business is demonstrated by the change in yellow that Calvin Grier (thewetprint.com) recently implemented. He used PY155 earlier, a benzimidazole yellow, but apparently his own testing proved that this wasn't as lightfast as the PY184 he is now using (or at least retailing) in his pastes. I don't doubt that the PY155 had excellent lightfastness ratings according to the manufacturer, otherwise I bet Calvin would have eliminated in earlier assays, but apparently his own testing proved otherwise.

It's a wormhole for sure, and I'm afraid there's no easy answer. There isn't even a complicated one that comes quickly - it appears the only real answer is a long and complicated one that takes a long time to arrive at.

Concerning your cyan: your blue & green mix sounds interesting. What problem were you trying to solve? For cyan so far I'm just using PB15:3 just like Calvin does and while I had some trouble before with it being on the blue side, I now seem to be hitting the same hue angle he does with his pigments, which is assuring. At least, if the pigment is properly dispersed and processed, which took me a week or two to figure out and resolve. I also find that in the pigment set I'm using (currently PB15:3, PR122 and PY154), the cyan PB15:3 actually has the highest tinting strength. I haven't looked into green pigments much yet, but if memory serves virtually all of the stable ones have lower chroma than PB15:3, so using a convenience mix of blue + green would logically not help all that much in realizing a larger gamut. Or am I mistaken?

[Vaughn]

Good you have found a good black! I have stayed away from using dry pigments...too lazy (and very happy with what I am using).

It is almost impossible to compare pigment loading of different pigment types usefully. I use 5 grams of Grahams lampblack per 750ml of water, which is 0.7%...ca 0.6 grams pigment per 10 grams of gelatin. The weight of my pigment also includes the binder (gum arabic, water and honey) and thus the tissue is very low contrast.

[bob carnie]

Bob, the best I can offer is something you probably already know about; the excellent overview of pigments compiled by Bruce MacEvoy at handprint.com; follow this one for the pigment index: https://www.handprint.com/HP/WCL/palette1.html It's conveniently grouped by color and within that on pigment code. You'll find the pigments in your Daniel Smith paint listed on the tube. He lists blue-wool scale ratings (not sure what source is he used) combined with his own testing (which he has done for a surprising number of pigments).

There's also this very comprehensive and easily accessible pigment database: http://www.artiscreation.com/Color_index_names.html
It consists of information compiled from several sources, including handprint.com, so to an extent it's redundant - but more comprehensive as it lists some pigments that handprint.com doesn't.

However, when it comes to permanence, I fear that figuring out how well your pigments will fare is a tricky proposition at best. The ratings provided by manufacturers or independent parties will give an indication, but if I look at the inconsistenties in some cases between for instance MacEvoy's findings and the industry-supplied ratings, it's clear that there are many nuances. Then there's the issue that a pigment of the same code (let's say PR122 or PB15:3) can differ between manufacturers, and as a consumer you never know what kind of differences there are - or even where the pigment you're using actually comes from. Relevant differences might be particle size or subtle chemical differences/impurities that can have an impact on the chemical stability of the pigment.

To make matters worse, sometimes, characteristics can be a blessing and a curse at the same time. For instance smaller particle size will generally result in higher tinting strength and higher chroma, but will also make the pigment more sensitive to chemical attack and hence fading, darkening or chroma loss.

I can imagine that further complications come from the way the pigment is used; there can be advantages (a matrix like gum or gelatin might protect the pigment locked inside of it) or disadvantages (traces of dichromate or other chemicals may form a threat to long-term stability). Long story short; it seems that the advice given by people like MacEvoy to do your own testing is probably not just a luxury, but an actual necessity if you want to determine if the pigments you, specifically, are using are sufficiently lightfast. I don't take it that far and just hope for the best based on the data I can find online.

That the lightfastness issue is hairy business is demonstrated by the change in yellow that Calvin Grier (thewetprint.com) recently implemented. He used PY155 earlier, a benzimidazole yellow, but apparently his own testing proved that this wasn't as lightfast as the PY184 he is now using (or at least retailing) in his pastes. I don't doubt that the PY155 had excellent lightfastness ratings according to the manufacturer, otherwise I bet Calvin would have eliminated in earlier assays, but apparently his own testing proved otherwise.

It's a wormhole for sure, and I'm afraid there's no easy answer. There isn't even a complicated one that comes quickly - it appears the only real answer is a long and complicated one that takes a long time to arrive at.

Concerning your cyan: your blue & green mix sounds interesting. What problem were you trying to solve? For cyan so far I'm just using PB15:3 just like Calvin does and while I had some trouble before with it being on the blue side, I now seem to be hitting the same hue angle he does with his pigments, which is assuring. At least, if the pigment is properly dispersed and processed, which took me a week or two to figure out and resolve. I also find that in the pigment set I'm using (currently PB15:3, PR122 and PY154), the cyan PB15:3 actually has the highest tinting strength. I haven't looked into green pigments much yet, but if memory serves virtually all of the stable ones have lower chroma than PB15:3, so using a convenience mix of blue + green would logically not help all that much in realizing a larger gamut. Or am I mistaken?

Hi Koraks

thanks so much I will look into Bruce MacEvoy as you list.
I do plan some tests myself to leave pigments in the outdoors for months on end and do LAB readings at time of printing and over time to see which of the pigments I use lose density.
I hope that the dichromates are removed with the wash process, as well one can do a metabisulfite bath at the end but I have no idea how to read the levels of AD in my finished gum prints
I use Calvins Cyan now , I am talking pre The Wet Print , Christina A and others recommended Thaylo Blue Green shade for cyan but it is a high staining pigment so I started custom mixing Viridian Green with a blue to get my cyan.
It was a PIA and am very happy with Calvins.

On a FB Gum page I have seen people use many types of colourant to make the colour and I think they have good possibilities.


Bob

[Drew Wiley]

Hi Bob. Can't talk much at the moment. But I do own a set of some extraordinary watercolor pigments sought out all over Europe and Africa by my late aunt, an expert on the subject, hand-ground by her, and of the highest permanence, better than any art store unless you're talking about just a couple speciality suppliers in Europe who might charge more per gram than gold for certain ingredients. But many of even those aren't impervious to the long-term effects of UV. That's why she only used them for sake of watercolor paintings etc, and never for her legacy public fresco murals, which mainly involved natural oxides. Even the concept of permanence is relative. Color which seems fresh in cave painting 40,000 years old, or in Egyptians tombs 3,000 years old, can quickly deteriorate once exposed to humidity shifts and UV-rich lighting. So try not to outlive your own prints, or you might be disappointed. When I'm done illustrating my own cave, I'll seal it off well.

[Vaughn]

That's the danger of carbon prints -- make a bad one and it can be around for a looooong time! Gelatin and carbon -- pretty tough stuff!

[Drew Wiley]

A few prints were actually recovered from the Titanic and a few other deep wrecks. Platinum prints, where the image is in the fiber itself, did a lot better than carbon, where the coating lifted off. One more reason not to display your prints on the walls of a sinking ship unless they're Pt/Pd.

[koraks]

Hi Koraks

thanks so much I will look into Bruce MacEvoy as you list.
I do plan some tests myself to leave pigments in the outdoors for months on end and do LAB readings at time of printing and over time to see which of the pigments I use lose density.
I hope that the dichromates are removed with the wash process, as well one can do a metabisulfite bath at the end but I have no idea how to read the levels of AD in my finished gum prints
I use Calvins Cyan now , I am talking pre The Wet Print , Christina A and others recommended Thaylo Blue Green shade for cyan but it is a high staining pigment so I started custom mixing Viridian Green with a blue to get my cyan.
It was a PIA and am very happy with Calvins.

On a FB Gum page I have seen people use many types of colourant to make the colour and I think they have good possibilities.


Bob
Hey Bob,

Great, thanks for the follow-up. Yes, many colorants would work and there are many ways to create a workable gamut. See e.g. Calvin's more recent work using natural pigments; it's a much more subdued, neutral palette than you'd get with high-chroma industrial pigments, but still (or perhaps, even more so) offers a very natural looking outcome. The creative possibilities are infinite. This is one of the things that has always drawn me to pigment processes.

As to the dichromate remnants: I've done some testing lately with carbon and my results were somewhat disconcerting. I noticed some color and chroma problems in my test prints, reached out to Calvin, who was extremely helpful, and he put me on the right track by pointing out dichromate stain might be the issue. I looked into it further using pointers he gave and did some testing of pure gelatin prints (without any pigment) at low and high dichromate concentrations to get an impression of the stain and how to manage it. Turns out that the stain is virtually impossible to remove, at least from my test prints onto Yupo. With just a wash, the stain remains of a yellow-orange hue, which implies it's still chromium-VI based and quite probably detrimental to print stability (not just the pigment, but possibly the gelatin and the support as well!) in the long term. Extended washing of several hours removes some of it, but not all...Reduction with bisulfite or ascorbic acid does effectively reduce the chromium-VI to chromium-III as evidenced by the hue shift towards a near neutral grey with a hint of lime. But there's still chromium metal left in the print and I'm not sure how problematic it is. The one thing that really 'helped' was to just use as low a dichromate concentration as possible...but evidently this has implications for tonal scale, pigment loading etc.
Here's the blog post I wrote about it a few days ago: https://tinker.koraks.nl/photography/how-to-ab-stain-dichromate-stain-issues-in-carbon-printing/
This is an illustration of the dichromate stain on some carbon-without-carbon (gelatin only) prints:
https://tinker.koraks.nl/wp-content/uploads/2022/11/Dichromated-gelatin-test.jpg
From top to bottom:
Print with 1% dichromate sensitizer; no substantial washing or clearing of the print. Note low level of stain; there's just not much chromium in there to begin with
Print with 16% sensitizer; note heavy staining. Unwashed and uncleared print.
Print with 16% sensitizer after soaking in water for a few hours. Note reduced but still present stain.
Print with 16% sensitizer after vitamin-C clearing bath (bisulfite does the same thing). Note reduced stain that has shifted to neutral hue.

When doing these tests my interests were more in the hue & chroma problems that come with stain and not so much the print longevity issue, so that's what I focused on.

PS: take he Lab* measurements on that blog page with a huge grain of salt as they were made with uncalibrated equipment. If you want I can give you some more accurate measurements made with the i1Pro I received recently.

[koraks]

Good you have found a good black! I have stayed away from using dry pigments...too lazy (and very happy with what I am using).

It is almost impossible to compare pigment loading of different pigment types usefully. I use 5 grams of Grahams lampblack per 750ml of water, which is 0.7%...ca 0.6 grams pigment per 10 grams of gelatin. The weight of my pigment also includes the binder (gum arabic, water and honey) and thus the tissue is very low contrast.

Yes Vaughn, it sure is difficult to make a meaningful comparison between pigments. So many factors influence the outcome. And there's always the question to what extent a comparison is necessary. Although there are two reasons why I do sometimes try. The first is to try and place my experiences into a broader context. If e.g. you mention a certain pigment loading or Sandy does in one of his writings, it's helpful for me to know what that actually means in practice. By having a bit of a reference in pigment loading, it's possible to estimate things like the kind of negatives you must be working with, what kind of relief you might be getting, what kind of exposure times etc. It's one of those parameters that indirectly says a lot about someone's process.

The other reason is just for consistency, which in my case is mostly about saving time. If I know that my 1% India ink to 8% gelatin tissue behaves in a certain way, it's nice to be able to translate that experience to a new pigment without having to do many test prints to figure out how strong the new pigment is.

Sadly, it's very difficult to do a good comparison, but it's possible to get in the ballpark nonetheless. What I generally do is make a 1% w/v solution of a pigment or a paint in water for the pigments/paints I want to compare. Then take two identical beakers with let's say 100ml water in each, and place 10 drops or so of the reference pigment solution into it. I then try to match the same tint by placing drops of the other pigment solution into the other beaker until they look more or less the same. In practice this gives a huge error, but the differences between pigments and paints are often so much huger still! For instance, the ivory black I trialed recently has perhaps 5% or 10% the tinting strength (if I'm generous!) of the lamp black that's in India ink or that constitutes the Kremer dry pigment I talked about earlier. That's such a huge difference that even with a large margin of error, a visual comparison as described above gives a useful insight.

[bob carnie]

Hey Bob,

Great, thanks for the follow-up. Yes, many colorants would work and there are many ways to create a workable gamut. See e.g. Calvin's more recent work using natural pigments; it's a much more subdued, neutral palette than you'd get with high-chroma industrial pigments, but still (or perhaps, even more so) offers a very natural looking outcome. The creative possibilities are infinite. This is one of the things that has always drawn me to pigment processes.

As to the dichromate remnants: I've done some testing lately with carbon and my results were somewhat disconcerting. I noticed some color and chroma problems in my test prints, reached out to Calvin, who was extremely helpful, and he put me on the right track by pointing out dichromate stain might be the issue. I looked into it further using pointers he gave and did some testing of pure gelatin prints (without any pigment) at low and high dichromate concentrations to get an impression of the stain and how to manage it. Turns out that the stain is virtually impossible to remove, at least from my test prints onto Yupo. With just a wash, the stain remains of a yellow-orange hue, which implies it's still chromium-VI based and quite probably detrimental to print stability (not just the pigment, but possibly the gelatin and the support as well!) in the long term. Extended washing of several hours removes some of it, but not all...Reduction with bisulfite or ascorbic acid does effectively reduce the chromium-VI to chromium-III as evidenced by the hue shift towards a near neutral grey with a hint of lime. But there's still chromium metal left in the print and I'm not sure how problematic it is. The one thing that really 'helped' was to just use as low a dichromate concentration as possible...but evidently this has implications for tonal scale, pigment loading etc.
Here's the blog post I wrote about it a few days ago: https://tinker.koraks.nl/photography/how-to-ab-stain-dichromate-stain-issues-in-carbon-printing/
This is an illustration of the dichromate stain on some carbon-without-carbon (gelatin only) prints:
https://tinker.koraks.nl/wp-content/uploads/2022/11/Dichromated-gelatin-test.jpg
From top to bottom:
Print with 1% dichromate sensitizer; no substantial washing or clearing of the print. Note low level of stain; there's just not much chromium in there to begin with
Print with 16% sensitizer; note heavy staining. Unwashed and uncleared print.
Print with 16% sensitizer after soaking in water for a few hours. Note reduced but still present stain.
Print with 16% sensitizer after vitamin-C clearing bath (bisulfite does the same thing). Note reduced stain that has shifted to neutral hue.

When doing these tests my interests were more in the hue & chroma problems that come with stain and not so much the print longevity issue, so that's what I focused on.

PS: take he Lab* measurements on that blog page with a huge grain of salt as they were made with uncalibrated equipment. If you want I can give you some more accurate measurements made with the i1Pro I received recently.

Very interesting... when you use dichromate with carbon where is it applied at the tissue making stage ? Its been so long since I did one I am embarrassed to say I forget the steps in a carbon transfer print.
I too am good friends with calvin I am in the middle of a big purchase from him, I tried the earth pigments for him with various success and will do more tests when I get through this busy period

[koraks]

I sensitize the tissue with dichromate just before exposing, using a foam roller, diluted with ethanol. It then needs to be exposed as soon as possible when dry, which is between around 45 minutes and a few hours for me.
Technically it's also possible to add dichromate to the glop when making the tissue but there are several drawbacks to this, so I don't bother.

I've only been in touch with Calvin briefly, but he's been really helpful indeed. I noticed your name in the acknowledgements of his Gum printing manual!

[bob carnie]

I sensitize the tissue with dichromate just before exposing, using a foam roller, diluted with ethanol. It then needs to be exposed as soon as possible when dry, which is between around 45 minutes and a few hours for me.
Technically it's also possible to add dichromate to the glop when making the tissue but there are several drawbacks to this, so I don't bother.

I've only been in touch with Calvin briefly, but he's been really helpful indeed. I noticed your name in the acknowledgements of his Gum printing manual!

I am a fan of Calvin , he is young and enthusiastic about materials I use...All I really did was look at his notes and made suggestions, some he took others not but its all good as far as I am concerned.

[koraks]

So am I; his enthusiasm is contagious and I think it's inspiring in any case that someone picks exactly this as a profession/career.