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 05:20 PM. Click to view previous post history.
Last night I made a small batch of emulsion for the latest matrix coatings. I included 3 drops of both FD&C Yellow 5 & FD&C Red 40 to act as extinction dyes. Yellow 5 (acid yellow 23, tartrazine) has peak absorption at 422nm and Red 40 (Allura Red) at 504nm. If anyone has spectral data on the red, I'd love to see it, as it is not in the Sigma-Aldrich handbook.
I don't know how effective this amount will be; the gelatin is red, but not exceedingly so. I have no idea what Kodak's matrix film looked like with the extinction dye, or how dark it has to be. We'll see...
If you are the big tree, we are the small axe
Regular Matrix film was yellow. It used Tartrazine alone.
As a side note, Pan Matrix film was black and used a soluble dye. Some claim that carbon was used to form the black and it remained. Well, here is the extended story as far as I can figure out. The early Pan Matrix was black and the dye washed out. This was so Pan Matrix and Matrix images were identical and could be compared. It allowed for easy reading of the gray scale that was included. Also, Carbon Black was made from burning tallow which imparted some harmful organics to the carbon mix. So, it was not used. In later years, pure Carbon Black was made available primarily for the image transfer products, and this was used as a permanent black image in Pan Matrix film along with the silver image.
I chose to add FD&C Red 40 kind of as an afterthought, since tartrazine's near UV absorption isn't great.
I had no idea pan matrix film was black; that's fascinating. Was the coating completely opaque? Thanks for.. the rest of the story
If you are the big tree, we are the small axe
Pan Matrix was panchromatic. It therefore had to have a black acutance dye just as tartrazine was the acutance dye for a blue sensitive film. It was not opaque, but rather translucent like Matrix film.
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Sure, that makes sense. It got me thinking though that a black pigment might have higher tinctorial strength and would have the added benefit of making the DCG matrices easy to identify.
Glad to know it was translucent, and yet still effective in its purpose.
I think carbon printers need to appreciate how easy this process would be to do, even with their existing glop. In fact, a matrix could be made in the typical transfer method onto a gelatin-free support. The gelatin would fog highlights as it would imbibe some dye.
Can't a carbon transfer more or less stick to any smooth surface? This would alleviate the need for a specially subbed product like the Estar Melinex.
Furthermore, it might result in sharper images; not having to expose through the base.
Just a thought...
If you are the big tree, we are the small axe
Exposure through the base is needed for any image that must adhere to the base. Exposure from the emulsion side is needed if one is to transfer the image. The acutance dye is needed to insure sharpness during exposure which is not materially decreased by exposure through the base.
With pan matrix, you could do an easy test strip with the red filter. You processed it and then slapped it onto a white tray to judge density. Because the emulsion carried tone, you could make a pretty good assessment of exposure for another test in 3 color that you would print. This same exposure test wasn't required with chromes because your chromes had so little exposure latitude.
H-burgers, you mention fogged highlights.This was an issue that was solved with a solution of Calgon water softener in the first rinse when printing. This made a huge difference in highlights and was (for most commercial labs) a default correction.
Exposing through the base + exposing sep negs through masks + stacking assorted post masks on the negs + making multiple incremental exposures with a register carrier -- all these things effected sharpness.
This is why point source lights were used with long focal length lenses (a 105 apo-nikkor was the industry standard for 35mm). Some of the challenges were minimizing diffusion, minimizing internal enlarger reflection, minimizing chromatic aberration.
PE, I've been thinking of the extinction dye as necessary for creating a thin relief, but does it also enhance acutance? I can see how that would be an added benefit!
Dewey, thanks for sharing that about the Calgon. Do you recall (roughly) at what concentration it was used? The chemical I was told helped with fogged highlights is sodium-hexametaphosphate, which also appears to be a water softener.
105mm on 35mm must have made for a tall enlarger. Did you also use wet-mount carriers and the like? The surgical precision of dye-transfer labs is somewhat intimidating to me. I hope I can get by with slightly less.
I plan to get into densitometry soon and really make sense of the system as a whole.
If you are the big tree, we are the small axe
I seem to remember that we mixed Calgon according to the instructions on the box and then added 5 - 10 mls per liter of first rinse depending on the amount of effect required.
Tartaro used the apo-nikkors on 8x10 Fotar enlargers modified with 5x7 Durst condensors and a low voltage pointsource. The chromes were suspended in mineral oil between glass.
Bob DeSantos had a lab in LA and he modified old Leitz Valoy enlargers for seps. If you haven't seen one of these, they have a very precise focusing system - more like a camera lens.
here's a picture: http://store.valueweb.com/servlet/vi...aloy-II/Detail
Bob wasn't too worried about his gear being pretty, so the point light was housed inside of a coffee can that has fitted to the Valoy. Since you're (typically) making your seps the same size for every job, the enlarger is locked and braced to the wall. I even had enlargers braced to a 4" pipe that was sunk into a concrete floor.
Originally Posted by Photo Engineer
Hi Ron and Chris - I just happend across these postings by accident. Very interesting Chris, I think that DCG matrices could work very well. I commend you for your work!
A few notes - please see my recent postings about paper mordanting on the Yahoo DyeTransfer group list server - the Kodak M1 mordant will work very well, and give very sharp prints with high DMAX. Fixed out paper works well, but isn't as sharp, particularly if you are making finished prints which are rewet one or more times for retouching purposes. I have been using fixed out paper (alum mordant) for test prints, and I give an additional M1 mordanting to the paper for final prints, for the best sharpness. Note - it is advisable to vigorously clean the paper surface with a very dilute photo flo solution before use to remove unwanted M1 mordant which can poison the matrix (cause the dyes to lock into the matrix,or back transfer into the matrix). This can be mostly eliminated with cleaning, but I would still recommend using a matrix clearing bath on all
While the Thorium Nitrate paper causes a Cyan hue shift to occur immediately, which can be desirable for quick evaluation of the color of the print without drying, the M1 mordant will actually give a much better correction of the Cyan dye hue than the Kodak paper, it is just that it doesn't occur until the print is dried. We have seen resulting blues, Cyans, and Greens which are much brighter than can be had on Kodak DT paper. M1 mordant - highly recommended if done correctly.
One note - the conditioner isn't really acidic, it tends to run neutral pH (7.0) to slightly acidic, pH 6.0. The idea is to have the paper more basic than the matrix, possibly causing electrostatic attraction of the dyes to the paper. If the pH of the paper is too low, no transfer would occur.
Regards - Jim Browning