That's a great point. The moment you get a landscape involved it totally falls apart. But for interior scenes; portraits and the like, it has a great warmth and beauty.
Capstaff's two-colour Kodachrome process.
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Chris;
When I was a teen and earlier, most grade B westerns were shot on a 2 color system which was horrible. That is one reason why GWTW and The Wizard of OZ were so spectacular, being shot in a 3 color system. It wowed me.
PE
When I was a teen and earlier, most grade B westerns were shot on a 2 color system which was horrible. That is one reason why GWTW and The Wizard of OZ were so spectacular, being shot in a 3 color system. It wowed me.
PE
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Two-color processes
Most color processes until about 1932 were two-color. You could make an exception for screen plates like Autochromes which would reproduce all three primaries or complimentaries, but even du Hauron's famous 1877 print of Agen, France appears to be a two-color process. Most colors we see in nature tend to be muted, or "blends" of the primary colors of blue, green and red. Rarely do we see an object that is pure blue or pure red or pure green, (or yellow, magenta or cyan for that matter). So when photographing natural objects like human faces or a hillside or a cow the process doesn't have to express a pure yellow or red. Unfortunately people noticed that you never saw a picture of a sunflower or the blue sky or an emerald which looked right and there developed a push for "full color".
In 1922 Technicolor had a great success with a two-color film which starred Anna May Wong called "The Toll of the Sea". Since it was set in China the producers apparently felt that people would think the limited color palette was just because those colors were popular in China. A mixture of dyes was used for the red and a mixture was used for the green elements, US patent 1807805. Two-color sequences occur in "The Phantom of the Opera" 1925, "Ben Hur" 1925, early talkies of Laurel and Hardy and the Three Stooges, When sound came in there was a flurry of two-color films. Parts of some prints survive: "Gold Diggers of 1929", "Follow Through", and "The Mystery of the Wax Museum". Other companies besides Technicolor preferred to work in two-color because it was much simpler. Kodak even manufactured a film stock for release prints with emulsion on both sides to facilitate the methods of these independent processes.
What hindered the introduction of a three-color "full color" process was the development of a camera which would take three separation negatives. No special camera was required for animation so Disney's cartoon, "Flowers and Trees" 1932 was a three-color process, probably the first from Technicolor. Most color cameras worked as bi-packs: two strips of film were sandwiched face to face. The front strip was blue sensitive only and it was dyed yellow to act as a filter. So the front strip only photographed blue light and then the yellow filter allowed only red and green light to pass to the rear strip of film, which was panchromatic.
However, the use of acid dyes when these films were printed allowed much richer colors to be presented, even in the two-color processes. It sort of made up for the lack of full color.
Most color processes until about 1932 were two-color. You could make an exception for screen plates like Autochromes which would reproduce all three primaries or complimentaries, but even du Hauron's famous 1877 print of Agen, France appears to be a two-color process. Most colors we see in nature tend to be muted, or "blends" of the primary colors of blue, green and red. Rarely do we see an object that is pure blue or pure red or pure green, (or yellow, magenta or cyan for that matter). So when photographing natural objects like human faces or a hillside or a cow the process doesn't have to express a pure yellow or red. Unfortunately people noticed that you never saw a picture of a sunflower or the blue sky or an emerald which looked right and there developed a push for "full color".
In 1922 Technicolor had a great success with a two-color film which starred Anna May Wong called "The Toll of the Sea". Since it was set in China the producers apparently felt that people would think the limited color palette was just because those colors were popular in China. A mixture of dyes was used for the red and a mixture was used for the green elements, US patent 1807805. Two-color sequences occur in "The Phantom of the Opera" 1925, "Ben Hur" 1925, early talkies of Laurel and Hardy and the Three Stooges, When sound came in there was a flurry of two-color films. Parts of some prints survive: "Gold Diggers of 1929", "Follow Through", and "The Mystery of the Wax Museum". Other companies besides Technicolor preferred to work in two-color because it was much simpler. Kodak even manufactured a film stock for release prints with emulsion on both sides to facilitate the methods of these independent processes.
What hindered the introduction of a three-color "full color" process was the development of a camera which would take three separation negatives. No special camera was required for animation so Disney's cartoon, "Flowers and Trees" 1932 was a three-color process, probably the first from Technicolor. Most color cameras worked as bi-packs: two strips of film were sandwiched face to face. The front strip was blue sensitive only and it was dyed yellow to act as a filter. So the front strip only photographed blue light and then the yellow filter allowed only red and green light to pass to the rear strip of film, which was panchromatic.
However, the use of acid dyes when these films were printed allowed much richer colors to be presented, even in the two-color processes. It sort of made up for the lack of full color.
The biggest problem with all of these was the fact that they were all reversal. Reversal print to print was and is pretty bad and continues to deteriorate from generation to generation. Therefore, special effects in color were virtually impossible and multi generational films were truly awful in tone scale. Well, the color got worse too.
I suspect that many of the 2 color films were so bad that they were released as B&W.
PE
I suspect that many of the 2 color films were so bad that they were released as B&W.
PE
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Early color cinema films were slap-dash processes. Most of the companies produced only a handful of examples. Even Technicolor let its quality control slip so much in the early 1930's that it hurt its brand. From what I understand it survived because a millionaire, Josh Whitney, underwrote the effort at producing a three-strip camera. Very few companies could equal the precision and high standards of EK--none ever surpassed EK. The fact is that most of them depended on EK manufactured materials. I don't know of any that made their own clear plastic base or coated their film.
The re-release market never had any money. Mostly it was just a bunch of itinerant projectionists traveling from town to town showing old prints on a bed sheet.
The re-release market never had any money. Mostly it was just a bunch of itinerant projectionists traveling from town to town showing old prints on a bed sheet.
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Pinatype dyes identified
Prof. John Wall in "Practical Color Photography" (1922 available online), on pp. 77-79 discusses the process and identifies the dyes used in the Pinatype dye transfer:
RED- natural carmine; lanafuchsin BB or SL;
BLUE- indulin blue for blue;
YELLOW-acid yellow, mikado yellow, or quinoline yellow.
Carmine is of course a well known colorant obtained from insects, C.I. 75470, aka Natural Red 4. (See first attached file thumbnail and also http://en.wikipedia.org/wiki/Carmine). It is likely that this is the dye used in Pinatype because the Pinatype dye and carmine both had to be mixed with ammonia before it was mixed with water and used. It is pink in color and would serve for the magenta.
Lanafuchsin BB has Colour Index number C.I. 16630 with this chemical description: 3-[(5-Acetylamino-2-methylphenyl)azo]-4,5-dihydroxynaphthalene-2,7-disulfonic acid disodium salt. There are illustrations of similar chemical structures, see Acid Violet 6, C.I. 16600.
Indulin blue, aka Acid blue 20, c.i. no. 50405. The structure is the second attached graphic.
Quinoline yellow, aka Food Yellow 13, D&C Yellow No. 10, Acid yellow 3, Quinidine Yellow KT, Japan Yellow 203, Lemon Yellow ZN 3, C.I. 47005
The structure is pictured in the third graphic.
I imagine that the first set of Capstaff Kodachrome dyes were similar in character.
Prof. John Wall in "Practical Color Photography" (1922 available online), on pp. 77-79 discusses the process and identifies the dyes used in the Pinatype dye transfer:
RED- natural carmine; lanafuchsin BB or SL;
BLUE- indulin blue for blue;
YELLOW-acid yellow, mikado yellow, or quinoline yellow.
Carmine is of course a well known colorant obtained from insects, C.I. 75470, aka Natural Red 4. (See first attached file thumbnail and also http://en.wikipedia.org/wiki/Carmine). It is likely that this is the dye used in Pinatype because the Pinatype dye and carmine both had to be mixed with ammonia before it was mixed with water and used. It is pink in color and would serve for the magenta.
Lanafuchsin BB has Colour Index number C.I. 16630 with this chemical description: 3-[(5-Acetylamino-2-methylphenyl)azo]-4,5-dihydroxynaphthalene-2,7-disulfonic acid disodium salt. There are illustrations of similar chemical structures, see Acid Violet 6, C.I. 16600.
Indulin blue, aka Acid blue 20, c.i. no. 50405. The structure is the second attached graphic.
Quinoline yellow, aka Food Yellow 13, D&C Yellow No. 10, Acid yellow 3, Quinidine Yellow KT, Japan Yellow 203, Lemon Yellow ZN 3, C.I. 47005
| IUPAC name[hide] Sodium 2-(1,3-dioxoindan-2-yl)quinolinedisulfonate |
I imagine that the first set of Capstaff Kodachrome dyes were similar in character.
Attachments
What kind of company are hinting at?
AgX;
Indulin blue fails the test of being a sulfonic acid. It has amino groups terminating it and thus is sold as the salt of an acid rather than being the acid itself. IDK how it would transfer compared to the other 2 dyes in the reference given which are sulfonic acids.
It would be nice if all of these dyes were azo dyes as well. Thus we could use one dye set for DT and DB imaging.
PE
Indulin blue fails the test of being a sulfonic acid. It has amino groups terminating it and thus is sold as the salt of an acid rather than being the acid itself. IDK how it would transfer compared to the other 2 dyes in the reference given which are sulfonic acids.
It would be nice if all of these dyes were azo dyes as well. Thus we could use one dye set for DT and DB imaging.
PE
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Companies making color film
AgX,
There were a wide variety of small companies who developed a color photographic process, particularly for movies. Usually they bought their raw stock from Kodak because EK was required by law to sell to its competitors, otherwise the government would sue EK for an anti-trust violation. All the classic Technicolor films, "Gone With the Wind", "The Wizard of Oz", "Snow White and the Seven Dwarfs", "Singing in the Rain", etc. were printed on Kodak release prints. Technicolor had developed a technique of dying a black and white release print into a full color release print. Technicolor did this for two reasons: 1) It wanted to be sure its release prints would run through a standard projector as well as a typical black and white film; 2) Technicolor used the same sound track as a black and white film. Typically Technicolor would print the sound track on black and white EK stock then DT the colors afterwards.
In the silent film days Technicolor appears to have manufactured its own film. The 1926 color film "The Black Pirate" with Douglas Fairbanks was shot with a special camera which recorded two-colors, called red and green, one every other frame. The camera negs were then step printed on to 70 mm stock, red images along the right side and the green along the left. The film was processed in some manner (relief matrixes? dye mordants?) and then the right side was dipped in a trough full of red dye and dried; then the left side was dipped into green dye and then dried. Next the 70 mm film was folded in half down the middle so the green image would overlay the red image in register. The two sides were glued together to form a 35 mm film which was run through the projector. Unfortunately, the film would peel apart and jam the projector. For this reason Technicolor developed the DT method.
In the silent era some companies hand painted their films; some used stencils; some used a rotating color wheel with red and green filters which rotated in synchronization in front of the projector lens. When sound came in some companies used a "bi-pack" camera, sandwiching two pieces of film face to face and running them through the camera as if they were a single piece of film. The front element was transparent and dyed yellow. It was sensitive to blue light but let red and green light pass through to the rear piece of film. Fox Studios produced such an experiment in 1929(?) which I saw: it was printed in blue and a ruby red--very natural. The Marx Brothers appear in a rare two-color process (on Youtube?) That would have been Paramount Studios. Brewster Color used dye toning; some examples of cartoons are on Youtube. Gaspar Color used a dye bleach method. He lacked a camera which would take separation negs, so his only US work is in stop motion, the "Puppetoons"--the most famous is "Tubby the Lonesome Tuba". This was a three-color process. I think Gaspar might have had his film manufactured in Europe. I don't believe he used EK materials.
Wikipedia has a good discussion of color cinema companies.
AgX,
There were a wide variety of small companies who developed a color photographic process, particularly for movies. Usually they bought their raw stock from Kodak because EK was required by law to sell to its competitors, otherwise the government would sue EK for an anti-trust violation. All the classic Technicolor films, "Gone With the Wind", "The Wizard of Oz", "Snow White and the Seven Dwarfs", "Singing in the Rain", etc. were printed on Kodak release prints. Technicolor had developed a technique of dying a black and white release print into a full color release print. Technicolor did this for two reasons: 1) It wanted to be sure its release prints would run through a standard projector as well as a typical black and white film; 2) Technicolor used the same sound track as a black and white film. Typically Technicolor would print the sound track on black and white EK stock then DT the colors afterwards.
In the silent film days Technicolor appears to have manufactured its own film. The 1926 color film "The Black Pirate" with Douglas Fairbanks was shot with a special camera which recorded two-colors, called red and green, one every other frame. The camera negs were then step printed on to 70 mm stock, red images along the right side and the green along the left. The film was processed in some manner (relief matrixes? dye mordants?) and then the right side was dipped in a trough full of red dye and dried; then the left side was dipped into green dye and then dried. Next the 70 mm film was folded in half down the middle so the green image would overlay the red image in register. The two sides were glued together to form a 35 mm film which was run through the projector. Unfortunately, the film would peel apart and jam the projector. For this reason Technicolor developed the DT method.
In the silent era some companies hand painted their films; some used stencils; some used a rotating color wheel with red and green filters which rotated in synchronization in front of the projector lens. When sound came in some companies used a "bi-pack" camera, sandwiching two pieces of film face to face and running them through the camera as if they were a single piece of film. The front element was transparent and dyed yellow. It was sensitive to blue light but let red and green light pass through to the rear piece of film. Fox Studios produced such an experiment in 1929(?) which I saw: it was printed in blue and a ruby red--very natural. The Marx Brothers appear in a rare two-color process (on Youtube?) That would have been Paramount Studios. Brewster Color used dye toning; some examples of cartoons are on Youtube. Gaspar Color used a dye bleach method. He lacked a camera which would take separation negs, so his only US work is in stop motion, the "Puppetoons"--the most famous is "Tubby the Lonesome Tuba". This was a three-color process. I think Gaspar might have had his film manufactured in Europe. I don't believe he used EK materials.
Wikipedia has a good discussion of color cinema companies.
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Pinatype dye structures
PE,
Capstaff's patents for his two-color process call for an "acid dye (preferably the salt of a sulfonic acid)", US 1196080; US 1315464. Only the dyes which you cited fit this description: lanafuchsin & quinoline yellow. The dyes carmine and indulin blue clearly are not sulfonic.
Pinatype dyes were used to dye the planographic matrixes over and over again. The matrixes could produce as many as twenty prints. The presence of aniline groups in indulin blue and the lack of SO3 groups in it and carmine indicate that these dyes diffuse more readily out of gelatin than dyes with more SO3 groups, groups which would have the effect of binding more substantially to the gelatin.
The Capstaff process was for "one off" assemblies of transparencies. While a dye transfer to blank paper over a period of ten to fifteen minutes would preserve the highlights, Capstaff required that the gelatin be thoroughly dried before dying, (Wall recommends drying for as long as three hours). A print surface so dried would be harder and much more likely not to absorb dye in the tanned highlights; even dyes with more affinity for gelatin such as salts of a sulfonic acid. It is possible that a wide variety of azo dyes which are salts of sulfonic acids would work in the Capstaff process. So a set of dyes suitable for DT and DB might be found.
PE,
Capstaff's patents for his two-color process call for an "acid dye (preferably the salt of a sulfonic acid)", US 1196080; US 1315464. Only the dyes which you cited fit this description: lanafuchsin & quinoline yellow. The dyes carmine and indulin blue clearly are not sulfonic.
Pinatype dyes were used to dye the planographic matrixes over and over again. The matrixes could produce as many as twenty prints. The presence of aniline groups in indulin blue and the lack of SO3 groups in it and carmine indicate that these dyes diffuse more readily out of gelatin than dyes with more SO3 groups, groups which would have the effect of binding more substantially to the gelatin.
The Capstaff process was for "one off" assemblies of transparencies. While a dye transfer to blank paper over a period of ten to fifteen minutes would preserve the highlights, Capstaff required that the gelatin be thoroughly dried before dying, (Wall recommends drying for as long as three hours). A print surface so dried would be harder and much more likely not to absorb dye in the tanned highlights; even dyes with more affinity for gelatin such as salts of a sulfonic acid. It is possible that a wide variety of azo dyes which are salts of sulfonic acids would work in the Capstaff process. So a set of dyes suitable for DT and DB might be found.
Gaspar had a special colour seperating cine-camera made. However it took three colour-separations in high-speed succession, what nevertheless hampered filming fast moving objects. Added by the low speed of that colour film system.
During Gaspar's European period hat silver-dye-bleach film was made by Gevaert.
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Falotico;
I am aware of those processes and patents. I was pointing out that Indulin Blue is not a sulfonic acid dye and therefore was probably not one that Captstaff really used. I also point out that a DB and a DT system could be built using the same dyes if they were all from the Azo dye family.
PE
I am aware of those processes and patents. I was pointing out that Indulin Blue is not a sulfonic acid dye and therefore was probably not one that Captstaff really used. I also point out that a DB and a DT system could be built using the same dyes if they were all from the Azo dye family.
PE
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A multi-use set of Azo dyes both for DB and DT would be very convenient. It might also be possible to combine the two processes: develop with a tanning developer, let the dye transfer into the whole matrix approximating the correct tones, and then bleach out the highlights.
From the language of the patents Capstaff seems to indicate that he uses only one dye per color. It also seems that his images from Capstaff Kodachrome were all assemblies requiring silver halide emulsions on transparent bases. I recall seeing a two-color portrait of George Eastman(?) from the 1920's which was published in the Time/Life book on photography called "Color", (1978). That gives some idea of the color values; the warm tones were somewhat orange. Looking through samples of dyes available at that time with the correct chemistry (acid dyes which form salts of sulfonic acids) it might be possible to rediscover the dyes that Capstaff used. The Colour Index gives structure, hue, lightfastness and date of discovery.
Capstaff invented two versions of DT: the first tanned the highlights with a bi-chromate bleach in the standard manner; the second tanned all the gelatin with ferric chloride and tartaric acid and then de-tanned the lowlights with a UV light image. I assume each version used different dyes. IDK which version the portrait in Time/Life "Color" used. I would love to see a Capstaff DT in the flesh.
I have seen examples of European Gasparcolor on Youtube. Gaspar moved here to California before the war and lived in Beverly Hills. He donated all his papers to UCLA and these are held by Special Collections. I wonder if he had Gevaert coat his films after the war. IDK who did that work for him.
From the language of the patents Capstaff seems to indicate that he uses only one dye per color. It also seems that his images from Capstaff Kodachrome were all assemblies requiring silver halide emulsions on transparent bases. I recall seeing a two-color portrait of George Eastman(?) from the 1920's which was published in the Time/Life book on photography called "Color", (1978). That gives some idea of the color values; the warm tones were somewhat orange. Looking through samples of dyes available at that time with the correct chemistry (acid dyes which form salts of sulfonic acids) it might be possible to rediscover the dyes that Capstaff used. The Colour Index gives structure, hue, lightfastness and date of discovery.
Capstaff invented two versions of DT: the first tanned the highlights with a bi-chromate bleach in the standard manner; the second tanned all the gelatin with ferric chloride and tartaric acid and then de-tanned the lowlights with a UV light image. I assume each version used different dyes. IDK which version the portrait in Time/Life "Color" used. I would love to see a Capstaff DT in the flesh.
I have seen examples of European Gasparcolor on Youtube. Gaspar moved here to California before the war and lived in Beverly Hills. He donated all his papers to UCLA and these are held by Special Collections. I wonder if he had Gevaert coat his films after the war. IDK who did that work for him.
All of the Capstaff work may now be at the George Eastman House.
As for a single dye set for both DB and DT, that is my goal as then you can match the prints using different methods. And, DB and DT materials are rather easy to coat yourself. None are in production at this time, but Jim Browning has posted a formula for the Matrix Film, and I have suggested elsewhere on APUG that a hardened version in a multilayer film or paper might be used for DB.
PE
As for a single dye set for both DB and DT, that is my goal as then you can match the prints using different methods. And, DB and DT materials are rather easy to coat yourself. None are in production at this time, but Jim Browning has posted a formula for the Matrix Film, and I have suggested elsewhere on APUG that a hardened version in a multilayer film or paper might be used for DB.
PE
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Jim Browning posts the three dyes he uses for DT along with his formula for matrix film at http://www.dyetransfer.org/. These dyes are:
Acid Blue 45- C.I. 63010
Acid Red 80- C.I. 69215
Acid Yellow 11- C.I. 18820
Only Acid Yellow 11 appears to be an azo dye, but it might be suitable for DB.
All the structures I can find for Chicago Blue are diazo (cf. Chicago Sky Blue 6B- C.I. 24410); the dye for the DB emulsion in "Photographic Emulsion Making" Solantine Pink is also diazo, C.I. 25380. Do the Chicago Blue or the Solantine Pink in this DB method transfer?
If I can get out to Rochester, NY I would like to see what I can at the George Eastman House.
Acid Blue 45- C.I. 63010
Acid Red 80- C.I. 69215
Acid Yellow 11- C.I. 18820
Only Acid Yellow 11 appears to be an azo dye, but it might be suitable for DB.
All the structures I can find for Chicago Blue are diazo (cf. Chicago Sky Blue 6B- C.I. 24410); the dye for the DB emulsion in "Photographic Emulsion Making" Solantine Pink is also diazo, C.I. 25380. Do the Chicago Blue or the Solantine Pink in this DB method transfer?
If I can get out to Rochester, NY I would like to see what I can at the George Eastman House.
Jim has used Solantine Pink and Solantine Yellow, as have I, for DB and for DT. The pink is a bit short but is rather like the old magenta in Ektacolor 70 paper.
So, the pink and the yellow both transfer and work with DB. What we lack is good information on a cyan, and we may need a better magenta.
PE
So, the pink and the yellow both transfer and work with DB. What we lack is good information on a cyan, and we may need a better magenta.
PE
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Isoelectric point of gelatin and dye absorption
Isoelectric point of gelatin and dye absorption. I came across a patent which describes the use of tanning developers to change the isoelectric point of gelatin and thereby make the developed image less able to absorb acid dyes. The invention is by David Dean and Robert Houck and they assigned the patent to EK: US Patent 2529922 (1948). They worked with dye-transfer (DT) relief matrix material which they exposed to an image and then developed in a tanning developer, either pyrogallol or hydroquinone. Ordinarily the gelatin has an isoelectric point at pH 4.7, but the oxidation products of the developers lower the isoelectric point of the gelatin composing the image to about pH 4.0 and leave the non-image areas of the gelatin at pH 4.7. Acid dyes which are dissolved in aqueous solutions at pH 4.7 will be absorbed by the non-developed gelatin, but will not be absorbed by the developed gelatin with the lower isoelectric point.
The principle has to do with the effect of acid/alkali solutions on the gelatin. The isoelectric point (IEP) is defined as the pH of the gelatin at which the positive charges in the gelatin are equal to the negative charges. If the gelatin is immersed in a solution of LOWER pH than the IEP--that is, a more acidic solution--then the gelatin will absorb more H+ ions than OH- ions, and consequently the gelatin will acquire a net positive charge. This positive charge will attract the negatively charged molecules of an acid dye. Acid dyes are anionic dyes. If the gelatin is placed in a solution whose pH is HIGHER than the IEP, than the H+ charges will be fewer than the negative charges in the gelatin. Consequently the gelatin will have an overall net negative charge which will repel the negative charges of the acid dye anions. (However, the gelatin will in this case attract molecules of BASIC dyes, which are cationic and positively charged).
Dean and Houck in their 1948 patent summarize these principles: if the IEP of the gelatin has a HIGHER pH than the solution containing ACID DYES, than the gelatin will absorb ACID DYES; if the IEP of the gelatin has a LOWER pH than the solution containing BASIC DYES, than the gelatin will absorb BASIC DYES; otherwise, the gelatin will not absorb the dyes. Dean and Houck used their invention to produce dye-transfer prints on a blank gelatin-coated paper.
CAPSTAFF AND PINATYPE PROCESSES. Both the Capstaff two-color process and the Pinatype dye-transfer process depended on using dichromate ions to harden gelatin. This formed the basis for selective absorption of acid dyes. In the Capstaff system, the photographic plate was exposed to the proper color record, then developed, bleached, hardened and dried. Finally it was placed in a weak acid dye bath and the dye would not be absorbed in any place where there had been a silver image. In other words, the dye would not be absorbed where the gelatin was hardened by reduced dichromate ions. But the dichromate reaction also lowers the IEP of the gelatin. I believe that the changed IEP also repels acid dyes in conjunction with the effect of hardening the gelatin--which hardening would make the acid dyes harder to absorb.
Similarly, in the Pinatype process, dichromate ions also harden the gelatin, but it this case through the action of exposure to UV light under a negative. The acid dye solution is not absorbed by the hardened parts of the gelatin. The dichromate matrix is then pressed onto a blank and the dyes transfer from the untanned portions onto the print forming a DT image. I suspect that here too there is a lowering of the IEP which repels the acid dyes.
I am aware that today isoelectric points are routinely analyzed in dye diffusion processes. I mention it here because I don't think that IEP changes have been considered as an aspect of the Capstaff or Pinatype processes. In the case of Pinatype this is because the Pinatype process was developed before the pH scale was invented. In the case of the Capstaff process, interest faded before IEP changes were understood very well in colloid science. As far as I know it was never considered as a cause of what was called in the 1920's "the Kodachrome effect."
Isoelectric point of gelatin and dye absorption. I came across a patent which describes the use of tanning developers to change the isoelectric point of gelatin and thereby make the developed image less able to absorb acid dyes. The invention is by David Dean and Robert Houck and they assigned the patent to EK: US Patent 2529922 (1948). They worked with dye-transfer (DT) relief matrix material which they exposed to an image and then developed in a tanning developer, either pyrogallol or hydroquinone. Ordinarily the gelatin has an isoelectric point at pH 4.7, but the oxidation products of the developers lower the isoelectric point of the gelatin composing the image to about pH 4.0 and leave the non-image areas of the gelatin at pH 4.7. Acid dyes which are dissolved in aqueous solutions at pH 4.7 will be absorbed by the non-developed gelatin, but will not be absorbed by the developed gelatin with the lower isoelectric point.
The principle has to do with the effect of acid/alkali solutions on the gelatin. The isoelectric point (IEP) is defined as the pH of the gelatin at which the positive charges in the gelatin are equal to the negative charges. If the gelatin is immersed in a solution of LOWER pH than the IEP--that is, a more acidic solution--then the gelatin will absorb more H+ ions than OH- ions, and consequently the gelatin will acquire a net positive charge. This positive charge will attract the negatively charged molecules of an acid dye. Acid dyes are anionic dyes. If the gelatin is placed in a solution whose pH is HIGHER than the IEP, than the H+ charges will be fewer than the negative charges in the gelatin. Consequently the gelatin will have an overall net negative charge which will repel the negative charges of the acid dye anions. (However, the gelatin will in this case attract molecules of BASIC dyes, which are cationic and positively charged).
Dean and Houck in their 1948 patent summarize these principles: if the IEP of the gelatin has a HIGHER pH than the solution containing ACID DYES, than the gelatin will absorb ACID DYES; if the IEP of the gelatin has a LOWER pH than the solution containing BASIC DYES, than the gelatin will absorb BASIC DYES; otherwise, the gelatin will not absorb the dyes. Dean and Houck used their invention to produce dye-transfer prints on a blank gelatin-coated paper.
CAPSTAFF AND PINATYPE PROCESSES. Both the Capstaff two-color process and the Pinatype dye-transfer process depended on using dichromate ions to harden gelatin. This formed the basis for selective absorption of acid dyes. In the Capstaff system, the photographic plate was exposed to the proper color record, then developed, bleached, hardened and dried. Finally it was placed in a weak acid dye bath and the dye would not be absorbed in any place where there had been a silver image. In other words, the dye would not be absorbed where the gelatin was hardened by reduced dichromate ions. But the dichromate reaction also lowers the IEP of the gelatin. I believe that the changed IEP also repels acid dyes in conjunction with the effect of hardening the gelatin--which hardening would make the acid dyes harder to absorb.
Similarly, in the Pinatype process, dichromate ions also harden the gelatin, but it this case through the action of exposure to UV light under a negative. The acid dye solution is not absorbed by the hardened parts of the gelatin. The dichromate matrix is then pressed onto a blank and the dyes transfer from the untanned portions onto the print forming a DT image. I suspect that here too there is a lowering of the IEP which repels the acid dyes.
I am aware that today isoelectric points are routinely analyzed in dye diffusion processes. I mention it here because I don't think that IEP changes have been considered as an aspect of the Capstaff or Pinatype processes. In the case of Pinatype this is because the Pinatype process was developed before the pH scale was invented. In the case of the Capstaff process, interest faded before IEP changes were understood very well in colloid science. As far as I know it was never considered as a cause of what was called in the 1920's "the Kodachrome effect."
Well, there are some problems here that were not fully understood or disclosed at the time of this patent.
IEP affects swell. In fact, IEP defines the minimum swell of a given gelatin and thus the point at which a minimum amount (or exact amount) of dye is absorbed. Change the IEP and swell changes. In fact, this trend goes counter to some of the points of the invention, but nevertheless, this change in pH was used to "bleach" dye from the mat reducing density or contrast.
Last but not least, you only discuss bone gelatin it appears, but at that time, they also used pig gelatin which has an IEP of about 9 and therefore this gelatin reacts totally differently to the conditions of the patent than bone gelatin.
I am not saying that they are incorrect, nor am I suggesting that this work is not useful, I am suggesting that there is a lot more to consider and a lot more going on than the patent suggests.
PE
IEP affects swell. In fact, IEP defines the minimum swell of a given gelatin and thus the point at which a minimum amount (or exact amount) of dye is absorbed. Change the IEP and swell changes. In fact, this trend goes counter to some of the points of the invention, but nevertheless, this change in pH was used to "bleach" dye from the mat reducing density or contrast.
Last but not least, you only discuss bone gelatin it appears, but at that time, they also used pig gelatin which has an IEP of about 9 and therefore this gelatin reacts totally differently to the conditions of the patent than bone gelatin.
I am not saying that they are incorrect, nor am I suggesting that this work is not useful, I am suggesting that there is a lot more to consider and a lot more going on than the patent suggests.
PE
Capstaff's two-color Kodachrome process.
P.E., this is off subject a little but some of National Geographic's earliest color pictures were made with a color process that, I once read, used dyed starch granules. Have you ever heard of this?...regards
P.E., this is off subject a little but some of National Geographic's earliest color pictures were made with a color process that, I once read, used dyed starch granules. Have you ever heard of this?...regards
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There are some good examples of the Capstaff color process posted on the internet. Interested people should take a look at them to see why there is so much interest:
http://americanhistory.si.edu/blog/...ctions-1914-kodachrome-of-george-eastman.html
http://image.eastmanhouse.org/files/GEH_1987_30_01.pdf
http://americanhistory.si.edu/blog/...ctions-1914-kodachrome-of-george-eastman.html
http://image.eastmanhouse.org/files/GEH_1987_30_01.pdf
You should note that the bulk of the photographs in your list above are portraits taken under controlled conditions.
The dyed starch grains were used in Lumiere film and plates.
PE
The dyed starch grains were used in Lumiere film and plates.
PE
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