Kallitype's & Zone VI Fix?

[Don12x20]

1) Paper makes a difference - in Dmax and exposure scale. HPR was the finest of 44 papers tested for Dmax.
2) Developer choice results in subtle differences in color for a given paper. You will see a couple of composite image tests in the upcoming book (to be published by Routledge in August).
3) Like Platinum/palladium, there is good reason to use a sequence of three trays for clearing after development - A sequence of disodium EDTA, Citric acid and then tetrasodium EDTA works well for archival permanence. Citric acid alone is insufficient to clear and can result in yellow staining and/or fading.
Don Nelson

Attached is an image showing average blurred colors for the ten developers tested on HPR. I cannot share the original images as my agreement with Routledge does not permit me to share the original. (But blurring will show the colors). Book will be available in August and is the result of extensive testing.
Top six - reading from upper left-ammonium citrate developer, borax developer. classic borax Rochelle salts developer, gray-blue tone developer, Henry Hall developer, Rochelle salt developer
Bottom four - reading from top (of the four) left - sodium acetate developer, 1/2 sodium acetate + 1/2 ammonium citrate developer, sodium citrate developer, warm brown-black developer.

 

[Don12x20]

And there is a chapter on Kallitype I wrote in this book https://www.routledge.com/Digital-N...hers-and/Reeder-Anderson/p/book/9780367862299

 

[Don12x20]

1) Paper makes a difference - in Dmax and exposure scale. HPR was the finest of 44 papers tested for Dmax.
2) Developer choice results in subtle differences in color for a given paper. You will see a couple of composite image tests in the upcoming book (to be published by Routledge in August).
3) Like Platinum/palladium, there is good reason to use a sequence of three trays for clearing after development - A sequence of disodium EDTA, Citric acid and then tetrasodium EDTA works well for archival permanence. Citric acid alone is insufficient to clear and can result in yellow staining and/or fading.
Don Nelson

Attached is an image showing average blurred colors for the ten developers tested on HPR. I cannot share the original images as my agreement with Routledge does not permit me to share the original. (But blurring will show the colors). Book will be available in August and is the result of extensive testing.
Top six - reading from upper left-ammonium citrate developer, borax developer. classic borax Rochelle salts developer, gray-blue tone developer, Henry Hall developer, Rochelle salt developer
Bottom four - reading from top (of the four) left - sodium acetate developer, 1/2 sodium acetate + 1/2 ammonium citrate developer, sodium citrate developer, warm brown-black developer.

here is what the series editor writes about the book:
Coming in August 2023!
Kallitype, Vandyke Brown, and Argyrotype is about photographic printing in silver on paper. These 19th and 20th-century processes provide contemporary artists with affordable ways to produce prints in silver. Prints can be additionally toned with gold, platinum, palladium, selenium, and other compounds to change the physical appearance and gain additional archival qualities normally achieved only through more expensive alternative process practice.
Kallitype, Vandyke Brown, and Argyrotype is a two-part book. Part One is a comprehensive how-to on these alternative processes. Part Two showcases the work of contemporary artists who print with these processes, accompanied by tips on their particular workflows.
Book features include:
* A brief introduction to each of the processes with key historical information.
* List of supplies and where to source them.
* How to set up the dimroom.
* Creation of digital negatives using the personal computer.
* Results of testing over 40 papers for suitability for kallitype, Vandyke brown, and argyrotype.
* Mixing formulas for sensitizers, fixers, kallitype developers, and toners.
* Images of resulting colors from developers and toners.
* Step-by-step how-tos on kallitype, Vandyke brown, and argyrotype.
* Troubleshooting kallitype, Vandyke brown, and argyrotype.
* Toning with noble metal toners (gold, platinum, palladium), selenium toners, and other suitable toners.
* Finishing prints for presentation.
Kallitype, Vandyke Brown, and Argyrotype provides both beginner and advanced alternative process practitioners with a concise guide for these three processes with the goal to encourage more practice of the “brownprint” in contemporary photography.

 

[MurrayMinchin]

1) Paper makes a difference - in Dmax and exposure scale. HPR was the finest of 44 papers tested for Dmax.
2) Developer choice results in subtle differences in color for a given paper. You will see a couple of composite image tests in the upcoming book (to be published by Routledge in August).
3) Like Platinum/palladium, there is good reason to use a sequence of three trays for clearing after development - A sequence of disodium EDTA, Citric acid and then tetrasodium EDTA works well for archival permanence. Citric acid alone is insufficient to clear and can result in yellow staining and/or fading.
Don Nelson

Attached is an image showing average blurred colors for the ten developers tested on HPR. I cannot share the original images as my agreement with Routledge does not permit me to share the original. (But blurring will show the colors). Book will be available in August and is the result of extensive testing.
Top six - reading from upper left-ammonium citrate developer, borax developer. classic borax Rochelle salts developer, gray-blue tone developer, Henry Hall developer, Rochelle salt developer
Bottom four - reading from top (of the four) left - sodium acetate developer, 1/2 sodium acetate + 1/2 ammonium citrate developer, sodium citrate developer, warm brown-black developer.

Thanks for chiming in.

Have the Reeder/Anderson book...looking forward to yours as well.

 

[Rolleiflexible]

1) Paper makes a difference - in Dmax and exposure scale. HPR was the finest of 44 papers tested for Dmax.
2) Developer choice results in subtle differences in color for a given paper. You will see a couple of composite image tests in the upcoming book (to be published by Routledge in August).
3) Like Platinum/palladium, there is good reason to use a sequence of three trays for clearing after development - A sequence of disodium EDTA, Citric acid and then tetrasodium EDTA works well for archival permanence. Citric acid alone is insufficient to clear and can result in yellow staining and/or fading.
Don Nelson

Attached is an image showing average blurred colors for the ten developers tested on HPR. I cannot share the original images as my agreement with Routledge does not permit me to share the original. (But blurring will show the colors). Book will be available in August and is the result of extensive testing.
Top six - reading from upper left-ammonium citrate developer, borax developer. classic borax Rochelle salts developer, gray-blue tone developer, Henry Hall developer, Rochelle salt developer
Bottom four - reading from top (of the four) left - sodium acetate developer, 1/2 sodium acetate + 1/2 ammonium citrate developer, sodium citrate developer, warm brown-black developer.

Don, while I concur with your second conclusion, that the developer affects print color even after toning, your first and third points do not correspond to my experience.

I have printed kallitypes extensively with the Hahnemühle Platinum and Revere Platinum papers, and I can detect no difference in Dmax and scale between them. I have settled on Revere because there is vanishingly little difference between the two, yet the Revere is a third less expensive than the Hahnemühle paper, and it is sourced from an American supplier.

As for EDTA, I avoid it because it bleaches out highlights, in ways that I could not retrieve through exposure adjustments. Others, including Sandy King and (I believe) Mike Ware, find no problem with citric acid as a clearing agent. On what are you basing your conclusion that two EDTA baths are required for archival images, and that citric acid clearing baths do not suffice?

FWIW, I first tried EDTA to clear prints when I started out, because I had been advised to double-coat my paper (Hahnemühle and Revere) before printing. Double-coating, I found, makes it nearly impossible to avoid image stains because the sensitizer is so thick. I tried EDTA (unsuccessfully) as a way to clear double-coated papers. Through a lot of trial and error, I found that double-coating leads to staining, and that a single coat of sensitizer, evenly applied, gives the same Dmax as a double-coated paper. I suspect double-coating leads to lasting iron residues in the paper, that cannot readiloy be cleared short of a long does of hydrochloric acid, with no corresponding advantage over a carefully-laid single coat.

Of course these are just my observations, based on my own experiences. I am sure you have your reasons for your conclusions. I look forward to reading your response, and your book.

Sanders

 

[Don12x20]

Don, while I concur with your second conclusion, that the developer affects print color even after toning, your first and third points do not correspond to my experience.

I have printed kallitypes extensively with the Hahnemühle Platinum and Revere Platinum papers, and I can detect no difference in Dmax and scale between them. I have settled on Revere because there is vanishingly little difference between the two, yet the Revere is a third less expensive than the Hahnemühle paper, and it is sourced from an American supplier.

As for EDTA, I avoid it because it bleaches out highlights, in ways that I could not retrieve through exposure adjustments. Others, including Sandy King and (I believe) Mike Ware, find no problem with citric acid as a clearing agent. On what are you basing your conclusion that two EDTA baths are required for archival images, and that citric acid clearing baths do not suffice?

FWIW, I first tried EDTA to clear prints when I started out, because I had been advised to double-coat my paper (Hahnemühle and Revere) before printing. Double-coating, I found, makes it nearly impossible to avoid image stains because the sensitizer is so thick. I tried EDTA (unsuccessfully) as a way to clear double-coated papers. Through a lot of trial and error, I found that double-coating leads to staining, and that a single coat of sensitizer, evenly applied, gives the same Dmax as a double-coated paper. I suspect double-coating leads to lasting iron residues in the paper, that cannot readiloy be cleared short of a long does of hydrochloric acid, with no corresponding advantage over a carefully-laid single coat.

Of course these are just my observations, based on my own experiences. I am sure you have your reasons for your conclusions. I look forward to reading your response, and your book.

Sanders

Sanders, thank you for your observations.

Papers - I have several lots of Revere collected over the years since they started offering. The best Dmax achieved was 1.38. However, the lots were variable (1.31-1.38). HPR achieves a consistent 1.41 across the samples that I have. There are other papers that are not widely available that can achieve 1.40 or even better Dmax - (Pergamenta parchment 110 at 1.47). And there is a small variance in paper results depending on which of the ten developers I used in testing. Note that the eye cannot detect the differences in dark areas as well as it does the differences in the highlight. I test with a reflection densitometer using step tablets and controlled environment.

Staining and use of EDTA: I have never seen highlight removal with disodium EDTA as the first bath - neither with all the 31-step tablet results nor with prints. I do use Tween20 in my sensitizer. You may find that adding a drop of Tween20 to your sensitizer will make a difference in your highlights, making the highlights more embedded in the paper fibers. Testing may help to see if you see a difference.

Ferric yellowing of paper is most noticeable if you mask the areas outside the print area and is almost unnoticeable if you all brush marks on your prints. It seems to occur after long periods of time and isn't evident even weeks after drying a print -- it takes years. I have kallitypes made in 1992 that were cleared in just citric acid, showing noticeable yellowing in these areas. I switched to clearing Kallitype with first bath Disodium EDTA after attending a Dick Arentz NA2 Platinum/Palladium workshop in 1995. I see no long term yellowing in those prints in the masked areas around the image.

Note that Pt printing also uses Ferric Oxalate as the sensitizer. So Kallitype suffers from the similar problems with ferrous removal even if acidic first baths are used so ferous hydroxl is not formed. A really good source for more information about the testing done on EDTA clearing of Ferric Oxalate sensitizer is found in "Platinum and Palladium Photographs-Technical History, Connoisseurship, and Preservation," edited by Constance McCabe (2016), published as a result of a Pt/Pd conference on preservation in Washington, DC.

Sandy and I have had a number of conversations as I tested and created the book. You will find that Sandy wrote the forward. (And Sandy and I collaborated on the Carbon Transfer book in the series.

As always, your personal results can vary from others based upon your local conditions and workflow. I merely report my personal results.

 

[Don12x20]

...and I never double coat the sensitizer.

 

[Rolleiflexible]

Sanders, thank you for your observations.

Papers - I have several lots of Revere collected over the years since they started offering. The best Dmax achieved was 1.38. However, the lots were variable (1.31-1.38). HPR achieves a consistent 1.41 across the samples that I have. There are other papers that are not widely available that can achieve 1.40 or even better Dmax - (Pergamenta parchment 110 at 1.47). And there is a small variance in paper results depending on which of the ten developers I used in testing. Note that the eye cannot detect the differences in dark areas as well as it does the differences in the highlight. I test with a reflection densitometer using step tablets and controlled environment.

Staining and use of EDTA: I have never seen highlight removal with disodium EDTA as the first bath - neither with all the 31-step tablet results nor with prints. I do use Tween20 in my sensitizer. You may find that adding a drop of Tween20 to your sensitizer will make a difference in your highlights, making the highlights more embedded in the paper fibers. Testing may help to see if you see a difference.

Ferric yellowing of paper is most noticeable if you mask the areas outside the print area and is almost unnoticeable if you all brush marks on your prints. It seems to occur after long periods of time and isn't evident even weeks after drying a print -- it takes years. I have kallitypes made in 1992 that were cleared in just citric acid, showing noticeable yellowing in these areas. I switched to clearing Kallitype with first bath Disodium EDTA after attending a Dick Arentz NA2 Platinum/Palladium workshop in 1995. I see no long term yellowing in those prints in the masked areas around the image.

Note that Pt printing also uses Ferric Oxalate as the sensitizer. So Kallitype suffers from the similar problems with ferrous removal even if acidic first baths are used so ferous hydroxl is not formed. A really good source for more information about the testing done on EDTA clearing of Ferric Oxalate sensitizer is found in "Platinum and Palladium Photographs-Technical History, Connoisseurship, and Preservation," edited by Constance McCabe (2016), published as a result of a Pt/Pd conference on preservation in Washington, DC.

Sandy and I have had a number of conversations as I tested and created the book. You will find that Sandy wrote the forward. (And Sandy and I collaborated on the Carbon Transfer book in the series.

As always, your personal results can vary from others based upon your local conditions and workflow. I merely report my personal results.

Don, thanks for your responses. In order:

I can speak only to papers in 2022 and 2023, during the time I focused on HPR and Revere, so I cannot speak to past variations in Revere's paper. Nor have I bothered to test with a densitometer. But I have printed many images with both papers, and I cannot see a difference in real prints. Tell me: Can you see the difference between a 1.38 Dmax and a 1.41 Dmax? At 65, perhaps my eyes are too old and tired to see what you readily perceive.

I do use a drop of Tween20 in the sensitizer. One of Clay Harmon's habits I internalized.

EDTA: I can speak only to disodium EDTA -- never tried the tetra version. But I have seen bleaching with disodium EDTA, especially with high-key images. I'm attaching a scan of a workprint (I gave away the final print, and threw away the bleached version) of the image that made me give up EDTA -- when I tried to clear it with EDTA, half of her face vanished, and did not come back up in the toner. I do not recall which paper, whether HPR or Revere -- it would have been one or the other.

I do routinely mask areas outside my prints -- I don't like brush marks. I have seen no staining in those areas since I stopped double-coating. FWIW, I develop using sodium acetate, clear in two 3pct citric acid baths, tone with (usually) platinum, and fix in TF4. I also wash liberally in water after development -- I am fortunate to have well water on the acidic side.

Does Sandy concur with the need to use EDTA in the clearing baths?

Sanders

 

[Rolleiflexible]

PS: I wonder whether the kallitype's susceptibility to bleaching from EDTA is a function of the developer used. When I had bleaching problems with EDTA, I was using a sodium citrate developer. I've since switched to sodium acetate -- don't know if/how that might affect image permanence in the presence of EDTA.

 

[Don12x20]

Sandy does not do Kallitypes any longer. When he did years ago, he always gold-toned. Both of us are primarily carbon transfer printers. Neither of us does kallitype now for personal work. We both use Vandyke Brown for fun, quick, and easy prints (good prints in just a few minutes after a quick sensitizer and exposure, compared to the days of materials prep for carbon!)

Both of us found that Vandyke brown is easier than kallitype (no developer!), produces the same results (color without toning is slightly different), and tones equally well compared to kallitype in gold, Pd, Pt, or selenium (either created by formula or using Kodak's rapid selenium) toner).

You can tell 1.38 from 1.41 if darks are placed next to each other, but otherwise, if just using the given paper, the darks will be acceptable to your eye, even if that paper only delivers a Dmax of only 1.25. I see lots of people's work on Facebook groups that use a paper for kallitypes (or VDB or Argyrotype) where they are not getting a good Dmax (or they don't know how to scan properly ;-)

One other thought - if you are using digital negatives and building your own curves to use with QTR, the testing sequence will build in any EDTA-created wash-off into the curve. You'll never see it. Similarly, it wouldn't be obvious if you do film/developer testing to match negative to process with a given developer dilution/time. You might give either a try.

As for your other questions, testing would start to help you answer your questions. My Nuarc 40-1ks died two days after I finished the final toner tests for the book (fortunately), and I am waiting for the delivery of my new Cone super-fast UV LED printer with a vacuum (needed for carbon). So I am currently unable to do any further testing to help you answer your questions.

Best regards!
Don

 

[Rolleiflexible]

Sandy does not do Kallitypes any longer. When he did years ago, he always gold-toned. Both of us are primarily carbon transfer printers. Neither of us does kallitype now for personal work. We both use Vandyke Brown for fun, quick, and easy prints (good prints in just a few minutes after a quick sensitizer and exposure, compared to the days of materials prep for carbon!)

Both of us found that Vandyke brown is easier than kallitype (no developer!), produces the same results (color without toning is slightly different), and tones equally well compared to kallitype in gold, Pd, Pt, or selenium (either created by formula or using Kodak's rapid selenium) toner).

You can tell 1.38 from 1.41 if darks are placed next to each other, but otherwise, if just using the given paper, the darks will be acceptable to your eye, even if that paper only delivers a Dmax of only 1.25. I see lots of people's work on Facebook groups that use a paper for kallitypes (or VDB or Argyrotype) where they are not getting a good Dmax (or they don't know how to scan properly ;-)

One other thought - if you are using digital negatives and building your own curves to use with QTR, the testing sequence will build in any EDTA-created wash-off into the curve. You'll never see it. Similarly, it wouldn't be obvious if you do film/developer testing to match negative to process with a given developer dilution/time. You might give either a try.

As for your other questions, testing would start to help you answer your questions. My Nuarc 40-1ks died two days after I finished the final toner tests for the book (fortunately), and I am waiting for the delivery of my new Cone super-fast UV LED printer with a vacuum (needed for carbon). So I am currently unable to do any further testing to help you answer your questions.

Best regards!
Don

Don, thanks for your reply. Since you are literally writing the book on kallitypes, I am trying to wrap my head around your conclusions. I appreciate you taking the time to respond in detail to my concerns.

To answer your question: I do print from digital negatives with curves built using QTR and Richard Boutwell's program, QuickCurve. I'm not sure how, practically, I could build a new curve to compensate for the "washoff" as you say, without throwing all the other values off. If -- if -- I found merit in using EDTA as opposed to citric acid for clearing iron, then I suppose it would be worth the effort.

What I am reading here, in your posts, is that you are not printing kallitypes, and you are basing your EDTA and citric acid experiences on prints you made in 1992 (with citric) and 1995 (following your 1995 Arendt workshop, with EDTA). Are these experiences the basis for your conclusion, now, that only EDTA can clear prints of iron? I do not doubt your observations. But as you know, papers change from year to year, and it is possible that your problems clearing with citric acid were a function of the paper you were using then. And as you said above, personal workflow matters a lot in these processes.

I am hoping you have a rigorous foundation for your conclusions. Can you explain how you've concluded that citric acid clearing baths cannot give archival results? Or that EDTA can?

You are publishing what is intended to be the authoritative book on this subject, that will guide printers for decades to come. Your conclusions are at odds with my experiences, but you speak with authority and I am trying, now, to wrestle the inconsistencies to the ground, and determine whether I need to throw out my own processes and start over. I do not have your years of experience in alt processes, but I have fully immersed myself in kallitypes the past couple of years and until your posts had thought to have mastered the process.

 

[Rolleiflexible]

Sandy does not do Kallitypes any longer. When he did years ago, he always gold-toned. Both of us are primarily carbon transfer printers. Neither of us does kallitype now for personal work. We both use Vandyke Brown for fun, quick, and easy prints (good prints in just a few minutes after a quick sensitizer and exposure, compared to the days of materials prep for carbon!)

Are you suggesting that your archival concerns about citric acid as opposed to EDTA are addressed by toning? I tone most of my prints with platinum. How (if at all) does that change your views of citric acid for clearing baths?

 

[nmp]

Don, thanks for your reply. Since you are literally writing the book on kallitypes, I am trying to wrap my head around your conclusions. I appreciate you taking the time to respond in detail to my concerns.

To answer your question: I do print from digital negatives with curves built using QTR and Richard Boutwell's program, QuickCurve. I'm not sure how, practically, I could build a new curve to compensate for the "washoff" as you say, without throwing all the other values off. If -- if -- I found merit in using EDTA as opposed to citric acid for clearing iron, then I suppose it would be worth the effort.

What I am reading here, in your posts, is that you are not printing kallitypes, and you are basing your EDTA and citric acid experiences on prints you made in 1992 (with citric) and 1995 (following your 1995 Arendt workshop, with EDTA). Are these experiences the basis for your conclusion, now, that only EDTA can clear prints of iron? I do not doubt your observations. But as you know, papers change from year to year, and it is possible that your problems clearing with citric acid were a function of the paper you were using then. And as you said above, personal workflow matters a lot in these processes.

I am hoping you have a rigorous foundation for your conclusions. Can you explain how you've concluded that citric acid clearing baths cannot give archival results? Or that EDTA can?

You are publishing what is intended to be the authoritative book on this subject, that will guide printers for decades to come. Your conclusions are at odds with my experiences, but you speak with authority and I am trying, now, to wrestle the inconsistencies to the ground, and determine whether I need to throw out my own processes and start over. I do not have your years of experience in alt processes, but I have fully immersed myself in kallitypes the past couple of years and until your posts had thought to have mastered the process.

You are toning with platinum - as long as there is no exposed silver in the print (i.e. to completion,) presence of iron is not detrimental to the image any more than a Pt-Pd print when cleared with CA only. The issue then is whether or not residual ferric/ferrous hydrolyses to form hydroxide - basically rust and yellow the print. For that you can test very easily. Take a piece of the paper that was coated, but not exposed (from the periphery of the image if using a something to block the UV) dunk it in a sodium carbonate solution and compare the color before and after. If there is yellowing, then the clearing is not adequate. Otherwise leave it be.

:Niranjan

 

[Rolleiflexible]

You are toning with platinum - as long as there is no exposed silver in the print (i.e. to completion,) presence of iron is not detrimental to the image any more than a Pt-Pd print when cleared with CA only. The issue then is whether or not residual ferric/ferrous hydrolyses to form hydroxide - basically rust and yellow the print. For that you can test very easily. Take a piece of the paper that was coated, but not exposed (from the periphery of the image if using a something to block the UV) dunk it in a sodium carbonate solution and compare the color before and after. If there is yellowing, then the clearing is not adequate. Otherwise leave it be.

:Niranjan

This is helpful. Can you be more specific about the sodium carbonate solution?

 

[Don12x20]

You are toning with platinum - as long as there is no exposed silver in the print (i.e. to completion,) presence of iron is not detrimental to the image any more than a Pt-Pd print when cleared with CA only. The issue then is whether or not residual ferric/ferrous hydrolyses to form hydroxide - basically rust and yellow the print. For that you can test very easily. Take a piece of the paper that was coated, but not exposed (from the periphery of the image if using a something to block the UV) dunk it in a sodium carbonate solution and compare the color before and after. If there is yellowing, then the clearing is not adequate. Otherwise leave it be.

:Niranjan

Niranjan - excellent test for sensitized areas that have been cleared. It is also non-destructive for images which leaves the print slightly alkaline after a good wash.

 

[nmp]

This is helpful. Can you be more specific about the sodium carbonate solution?

Just the standard 1% (10g/liter) solution that one would use for bleaching cyanotypes, for example. Actually, you don't need much. Just a few drops on the paper, leave it for a few minutes and then wash. If there was any iron left, there should be a discoloration at the treated spot. Ferrous hydroxide is green but it will oxidize readily in air to become red/yellow ferric hydroxide.

:Niranjan.

 

[BHuij]

Fascinating thread, I'll be following carefully. I also have been doing kallitypes for a lot less time than Sandy or Don, but long enough to have found a curve that is giving me excellent results with inkjet negatives on Pictorico. I can detect zero evidence so far of insufficient clearing in any of my prints. I single coat on HPR, develop in sodium citrate for 3 minutes, rinse twice in mildly acidic tap water for 1 minute each, and then clear in 3% citric acid for 5 minutes before moving on to gold toning. My whites are paper base white and match the areas of the paper that got no sensitizer when everything is said and done. I also get a good Dmax (not comparable to silver gelatin, but deep enough to satisfy my goals with this process), good tonal separation in the shadows, and highlights up to paper base white where desired.

But perhaps my prints just aren't old enough to display any of the problems related to insufficient clearing.

FWIW for the OP, I am using the sodium thiosulfate (with a few other minor additions of sodium sulfite and sodium carbonate IIRC) that Sandy King recommends in his article.

Also possibly of note to OP - unless you're not planning on toning your kallitypes at all, I wouldn't judge your test strip "minimum exposure time to Dmax through film base" time until after you have fully processed your test strip print, including toning, and allowed it to dry. Kallitypes are known to solarize, so it's not odd to see what looks like dmax at, say, 4 minutes, and then the longer exposures actually look like they're getting lighter. This doesn't mean that you have hit dmax in 4 minutes. The solarization is reversed by the toning.

 

[tnp651]

1) Paper makes a difference - in Dmax and exposure scale. HPR was the finest of 44 papers tested for Dmax.
2) Developer choice results in subtle differences in color for a given paper. You will see a couple of composite image tests in the upcoming book (to be published by Routledge in August).
3) Like Platinum/palladium, there is good reason to use a sequence of three trays for clearing after development - A sequence of disodium EDTA, Citric acid and then tetrasodium EDTA works well for archival permanence. Citric acid alone is insufficient to clear and can result in yellow staining and/or fading.
Don Nelson

Attached is an image showing average blurred colors for the ten developers tested on HPR. I cannot share the original images as my agreement with Routledge does not permit me to share the original. (But blurring will show the colors). Book will be available in August and is the result of extensive testing.
Top six - reading from upper left-ammonium citrate developer, borax developer. classic borax Rochelle salts developer, gray-blue tone developer, Henry Hall developer, Rochelle salt developer
Bottom four - reading from top (of the four) left - sodium acetate developer, 1/2 sodium acetate + 1/2 ammonium citrate developer, sodium citrate developer, warm brown-black developer.

Don,
I have seen good results with citric alone but the thought of eventual yellowing is deeply concerning. Can I clear old prints, some a couple of years old, in EDTA? Will I see bleaching of the highlights (I always use TWEEN)?
Tom Nelson

 

[Rolleiflexible]

Don,
I have seen good results with citric alone but the thought of eventual yellowing is deeply concerning. Can I clear old prints, some a couple of years old, in EDTA? Will I see bleaching of the highlights (I always use TWEEN)?
Tom Nelson

FWIW I used TWEEN in my sensitizer when I experienced bleaching with EDTA. Of course this is anecdotal based on my own experience.