Color Dye-Transfer Prints for the Modern Hobbyist - *Imbibition for For the People!*
HISTORY of the PROCESS
In 1994 Kodak discontinued the "Kodak Dye-Transfer Process". Since that time, only those who have hoarded those materials or have been enterprising enough to manufacture their own silver-halide matrix films (Jim Browning) have been able to make dye-transfer prints.
However, this is a curious & unfortunate state of affairs! The earliest dye-transfer (or dye imbibition) prints were made by exploiting the same mechanism that modern day carbon & gum printers use; the ability of potassium or ammonium dichromate to harden gelatin upon exposure to UV light.
The 2 most common ways to a make a dye-imbibition print both rely upon a gelatin matrix.
In recent times (Kodak) the preferred method was with a silver-halide emulsion on a clear base. A negative is exposed through the base and developed in a tanning developer which hardens the gelatin in situ with the developed silver. This is then "etched" in hot water, which removes the gelatin that remains untanned (soluble) to reveal a relief image that clings to the base. This gelatin relief consists of varying depths that correspond directly the shadow density in the photograph.
The other method is very similar, but instead of using a silver-halide emulsion, a gelatin layer is sensitized with dichromates and exposed (again, through the base) under a negative and etched in hot water. It is this variable gelatin relief that absorbs dye to varying degrees, thus continuous tone is possible.
An obvious difference between these 2 methods is that the silver-halide emulsion can be exposed under an enlarger whereas the DCG (dichromated gelatin) requires an enlarged negative for contact printing. This is one important reason for the success of the silver-halide method.
However, the use of DCG matrices has many precedents, most notably the Pinatype process; outlined here in this British Journal of Photography article from 1907. However, the first application of this property that gelatin will imbibe & transfer a dye was disclosed by Charles Cros, a Frenchman, who called it the Hydrotype process in the late 1800's. Another process was Jos Pe. It should be noted that the Pinatype uses a slightly different type of matrix (one that is not etched = planographic, as opposed to relief) and correspondingly uses a different class of dyes and is exposed under positives, interestingly enough. No need to go into this in depth at the moment however....
So, to make a dye-transfer print, a relief matrix is soaked in a bath of an acid-dye, the dye imbibes (or migrates) into the gelatin relief image and this is then rolled into contact with a sheet of receiving paper. The dye transfers from the matrix to the receiving paper.
If 3 matrices are prepared from color separation negatives, and dyed in the appropriate secondary dye colors (CMY), and finally transferred in register to the receiving paper, a full color image is formed. This is the process in a nutshell.
Although my work on this technique is far from complete, I want to at least disclose and compile all the information so far gathered, so that other people who are interested may join the effort.
- PREPARING THE MATRICES
First, the modern worker needs a suitable clear support. This is found in Photo Formulary's Estar Melinex (mispelled on their website as 'melenex'). This is a thin, clear support that is subbed to accept emulsions. This subbing cannot imbibe any dye itself, which is ideal becaue otherwise you will get stained highlights. Although I have not tested any other materials, I'm curious what else might be suitable. Overhead transparency paper perhaps? Whatever the substrate is, it must be treated so that it "grabs" the gelatin, otherwise it will easily peel off. Search "corona discharge" for more on this, or APUG member hrst's work with substrates. Fortunately, there is an existing product at the moment.
The melinex scratches easily, and care should be taken to keep it as unblemished as possible. Vaseline or some kind silicon oil (PE) might be able to hide the scratches when it comes time for exposure (remember, we're exposing through the base).
As a side note, another option would be to do a "carbon transfer" of the clear relief image (or pigmented relief image for that matter) and this could become the matrix. This would eliminate the need for exposing through the base and a special substrate for the matrix.
2nd, you must coat the melinex with a gelatin layer. This is effectively no different than pouring carbon tissues (sans pigment). I have chosen 6% gelatin with 1% sorbitol, though there is nothing yet to suggest that this is superior to any other concentration, and not enough testing has been done to see what effect the gelatin composition will have upon the matrix characteristics. This gelatin solution pours nicely and makes a thin coating; this has been my only criteria so far. Each worker will probaly find their preferred way to achieve this, just like in carbon pouring.
3rd, the matrix blank must be sensitized. Having very little experience with this personally, I can only say that it will be necessary to have the back surface clean of any splotches before exposure, and also the deepest layers of the gelatin must be sensitized. It has been suggested (Vaughn) that this is not really a concern.
Fortunately, the rigid densitometric requirements of traditional dye-transfer printing can likely be thrown out the window when using DCG matrices. Traditional AgX matrix films had but one contrast grade, necessitating strict control of contrast in the sep negs. Thanks to the contrast control available from dichromate sensitization, considerable leaway should be had.
Chalk one up for DCG-imbibition!
4th, UV exposure under negatives. The ins & outs of making color separations are best left alone in this discussion, but tri-color gum printers will probably find their negatives excellent for preliminary testing. I am exploring the route of making enlarged negatives on mammography x-ray film (with an intermediate panchromatic step), which so far has proved promising.
5th, etching in hot (120°F) water, just like carbon. Due to the nature of the hardening by dichromates, control should be exercised to ensure consistency. This difficulty is eloquently (if not somewhat discouragingly) described in this post.
6th, at this point, one should probably clear (sodium sulfite?) the matrices and perhaps harden them. However, I can't recommend anything at the moment. Some hardeners, like chrome alum, might act unfavorably as mordants in the matrix, where we don't want them. Will advise.
As it stands now, obtaining appropriate dyes is the single biggest roadblock. Recently, a couple boxes of Kodak dyes came through eBay and sold for over $100 a pop. Not a sustainable solution.
Jim Browning has listed the following dyes in his PDF for Dye Transfer Materials: Acid Blue 45 (or 25; bluer and transfers slower), Acid Red 80 (or 289*), Acid Yellow 11 (or 23*) [*brighter colors at the expense of light-fastness].
J.S. Friedman, author of the monumental "History of Color Photography", lists a number of textile dyes that may be suitable for the process and I would encourage people to explore that route. Although the color demands might not be perfectly met, textile dyes are easily obtainable and might be perfectly satisfactory for the imaginative printer. These textile dyes, known as "Acid Fast", will likely work and are available very cheaply. I suspect that their light-fastness is good if they are well regarded by textile folks.
Many sellers on eBay have large quantities of dyes, usually being liquidated from old labs, etc. All dyes have multiple names, so consult a book like Sigma-Aldrich's Handbook of Stains, Dyes & Indicators (easily available from most University libraries) to find out alternate names, chemical information, lightfastness and color quality.
The best option might be to find a manufacturer that offers samples of their dyes. A sample is likely to be sufficient for many, many prints, or alternatively, you might wish to see what their minimum quantity is.
When all is said and done, availability of dyes will be the key to truly making modern-day dye-transfer a reality. I am fortunate to have a wide variety of old dyes given to me by a chemist who researches dye-transfer, in addition to synthesizing his own dyes. So, perhaps there is hope that in the future we can provide better options in this regard. In the meantime, I will use these dyes to test my materials and will be simultaneously exploring alternative dye options, such as textile dyes.
A word about dyes: acid dyes happen to have an affinity for gelatin, that is, they will stain it. This affinity is increased with lower pH (more acid), and thus the receiving paper is soaked in an acid solution to encourage the dyes to leave the matrix and transfer more completely. Logically enough, to clear the matrix after transferring, a dilute ammonia solution will liberate the dye from the gelatin. A matrix can be reused many times, another reason why this process was so successful (ultimately superceding carbro in the industry).
There have been other methods to make prints with different classes of dyes like Pinatype above, which used "Pina" dyes... a.k.a. a proprietary dye (though Friedman lists the probable candidates). Also, there have been methods to use basic dyes, which are exceptionally brilliant & pure, but are very quick to fade. Since these dyes react differently with gelatin, different materials & methods are required. See Friedman if interesetd.
But acid dyes are the preferred class because they are quite good in color, and are the most permament of dyes. Other dyes that will act in the same manner as acid dyes are "direct" and "reactive" dyes, though I am far from an expert on these matters.
For an excellent paper on the requirements & testing of dyes, please follow these links -> Part 1, Part 2, Part 3, to Dyes For Imbibition Printing by Colton & Thronson.
Any information on dye-transfer printing, such as that given by Jim Browning, or Ctein, or Kodak's publication E-80 will give you a solid idea of what is necessary for transferring the print, as this function is independant of the kind of matrix used. At the moment, this is my least studied area of the process so I'd hate to give misinformation. It is however, pretty straight forward.
Basically you soak the matrices in their respective dye baths until they reach equilibrium (that is, the time it takes to absorb all the dye that they can hold). Then, you transfer them to a dilute acetic acid bath of about 2%. This rinses the excess dye off. At this point, in the acid bath, the dye will not exit the relief, and if the 3 matrices are not registered yet, they can be visually aligned in this bath and punched. The color image will be visible at this point.
Each matrix is then rolled onto the receiving paper, one after the other. The time that it takes for the dye to exit the matrix and migrate to the receiver paper will be a function of the dye, and will likely vary (as it did in the Kodak process). Standard practice is to transfer each color twice.
Another important aspect is the receiving paper itself and the pre-treatment bath. Kodak supplied a pre-bath for the receiving paper, but at the moment I couldn't tell you exactly what is in it. It stands to reason that it would be an acidic bath, and indeed, a sloshing of vinegar (not very scientific, nor ideally probably) helped a down & dirty test succeed while testing with a food dye. See here.
So as you can see, considerable room for experimentation is present. For initial testing, fixed out photo paper will be more than sufficient and actually the hardeners present in the emulsion, or from some fixers, will act as mordants in their own right.
An idealized receiving paper will have a dedicated mordant. F.E. Ives first suggested this method in U.S. patent #1,121,187, 'Photographic Printing Process', from December 15th, 1914. Basically, the mordant increases the paper's affinity to hold onto the dye (from the French word mordere, "to bite").
F.E. Ives has many earlier patents describing the use of DCG matrices for imbibition printing. Friedman doesn't spend much ink in discussing dye-transfer matrices of this type, instead simply saying that F.E. Ive's patents on the subject can be considered the authoritative text. Indeed, I would recommend anyone interested to seek them out, and I'll be more than happy to include the patent #'s. (p.s. They are listed in Friedman, and that book is available on Google books).
So as you can see, the work is just beginning. But all the information is out there and nothing is beyond the scope of the hobbyist. It just isn't formalized as of yet, so there is a lot of original & novel work that must be done before we can start "spreading the gospel" and telling people exactly how to do it.
I hope this will encourage a few people to give it a go, and remember that if tri-color seems daunting, there's certainly nothing wrong with monochrome prints. That would greatly expand the list of possible dyes for the process.
More to come in the future...
- Chris Holmquist, holmburgers, 2011 -
Last edited by holmburgers; 05-25-2011 at 04:20 PM. Click to view previous post history.
Holy smokes! That's a commitment. Unfortunately, the product was subpar at the end of its life. Because it was not a money-maker, production was delegated to new staff who didn't even know what it was used for. I spoke to a couple of engineers who inherited the product and it was obvious that Kodak was continuing low-level production until they were certain there would be no legal issues with discontinuing it - can't really blame them. I hope the batch that Ctien bought was up to standard.
I agree with you. There's lots of ways to skin a cat, but the direct method is always best. The Vericolor method was always unsatisfactory. The interpositive/negative method could be good and provided lots of control, but lacked the richness of Pan Matrix.
This is pretty disheartening to me, too.
Originally Posted by holmburgers
Dewwy, can you explain why the no longer existent Pan Matrix film worked, but others are fraught with trouble?
Pan Matrix was aimed at the market of advanced color darkroom users - portrait, landscape, wedding photographers and artists. Labs never really embraced it because the busy/successful ones had their hands full making dyes from transparencies for ad agencies (a much more lucrative market).
Pan Matrix was relatively simple when compared to the other methods. Direct exposures were made onto 3 matrix films through red, green and blue filters. The film was available in 14x17 and another larger size - prepunched for registration. You could use a standard B+W enlarger with a glass or oil carrier to keep your neg from moving, expose your 3 mats, develop in Kodak tanning developer and then you're ready to print.
They stopped making this product a few years before they discontinued the entire dye transfer product line. There simply wasn't a market for it.
I've made dyes from negs using Pan Matrix and by making interpositives. With a very good quality neg, you can't beat Pan Matrix, however the separation method allows for infinite control. One of the last ones I made used over 140 sheets of film for all the masking I did on an underexposed neg. Today you would just crank some curves in PhotoShop.
Separation Positives from C-41 Negatives
So back to C-41 neg's for a moment... a while back I calculated the average density of a well exposed C-41 negative, ≈5.5.
My thinking is to measure the incident light at my baseboard, and contact print a 4x5" C-neg onto b&w pan film, applying this density as a kind of filter factor. From the incident reading you use f/1 for your exposure time (since there is no aperture to attenuate the light), apply filter factors for the Wratten filters being used and also reciprocity-failure corrections. Ideally the exposure times should all be the same, so perhaps apply ND or if you're using an enlarger as the light source, adjust the aperture.
This should get in the ballpark of properly exposing a C-41 separation, and if I take 2 bracketed shots of each separation to give me 6 total sheets I can develop them all at once in my MOD pro-plates 4x5" processor.
Now.. am I missing something? Sure a C-41 negative 'looks' different, but what is so fundamentally difficult about making a positive separation from it? Does the mask skew the balance of light so that each layer requires a radically different exposure and if so, wouldn't that be fairly constant, thus allowing you to apply whatever skew there is across the board?
If you've got a set of good, straight-line, separation positives, these can be projected onto X-ray film to make the enlarged negatives. At least that's the plan...
One last thing of tangential interest that I'll add... the old Pinatype process required separation positives to make dye-imbibition prints. This is because it used a planographic matrix as opposed to a relief matrix. This is exactly the kind of a matrix used in bromoil/oil printing, wherein there is no hot-water etch and you're left with an image of untanned & tanned gelatin. Since this was under a positive, the highlights are tanned and thus do not imbibe liquid so easily, whereas the "soft" gelatin in the shadows does. The obvious discrepancy here is that the tanned gelatin of a relief matrix clearly accepts dye, so how are we supposed to get clean highlights? The key is in the dye itself. The Pinatype process used a different class of dyes, proprietarily known as "Pina dyes"; the chemical structure having never been disclosed. However, dyes with this property are known and in Friedman's book. Figuring out a planographic-matrix imbibition scheme would allow you to make prints from positives.
But I include this mainly for historial interest, unless of course someone wants to take it upon themselves!
If you are the big tree, we are the small axe
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Put a small step tablet in the border of the C-41 neg so you can measure shadow and highlight density through the negative film base. Red and green can probably be developed the same, but blue will need significantly more processing time. You may be right about the mask skewing the balance - all I can tell you is that unlike a transparency, each neg will be dramatically different.
Once you have your interpositives, a set of gamma one negs is cake.
Sounds good, I will give that a try with the step tablets.
I'm interested in why the blue filter separation needs the extra development. What exactly does it accomplish? (sorry, I'm pretty wet behind the ears when it comes to H&D kind of stuff).
When you 1st mentioned it, I thought I heard a bell ringing somewhere in my head.... check out this line from instructions for the Pinatype process, "The separations are first converted into positive transparencies. These, with the exception of the yellow, should be very soft, hence they might be made upon a color-blind negative material. The yellow image should be developed fairly hard."
If you are the big tree, we are the small axe
I can't tell you why, but it's consistent through many processes. Maybe panchromatic material has a lower inherent gamma in the blue sensitive range. The red and green are also different, but not worth addressing for your current tests.
If color negatives varied in balance this would be a tragedy and would renter neg-pos systems untenable in the industry. As it happens, Kodak has maintained the same balance with negatives from the first to present, and I can print them on color paper with nearly the same balance. The same holds true for dye transfer from what I could glean back in "the day".
The R/G/B speeds of the various color negative films are kept in as much control as are positive films in order to simplify all varieties of color printing, and with the exception of CU Color Negative from the 60s, all color neg is controlled. So, if you have trouble printing using color negatives, the problem is elsewhere than in the negative.
However, printing with R/G/B separation filters either from color positives or color negatives is a true pain. The best way is to use a special tricolor camera that does the job for you taking the original.
Sounds like my experience in making seps from color negs wasn't as good as yours.
The "one shot" camera was certainly easier than making seps from a chrome or neg, but the image size was rarely consistent, so you had to fiddle with enlargement size to keep the matrix films in register. You also (ideally) had to do substantial postmasking to address color and contrast issues.
Holmburgers, those digital sep. negs are looking a lot better. In fact, Tartaro was experimenting with a hybrid digital neg dye transfer at the end of his career. Digital meant (even then) a lot of color and curve control + no flare.
My experience was vicarious via Louie, Spot and Ctein.