I've got a series of photos I'm working on, which I think will look best as salt prints. Up until this past year, I mostly printed on glossy fiber paper, but after seeing some salt prints and palladium prints a friend made, glossy just isn't doing it for me anymore, and I've come to really like the look of alt processes where the image is embedded in the paper.
There's one issue for me with traditional alt processes though, and thats contact printing. I shoot 8x10, so contact printing is possible, but I love big prints. I'd like this series to be at least 16x20, and maybe even 30x40, but as the shots are landscapes mostly, hiking around with a 30x40 camera would be a bit challenging. I know making large internegs is possible, but as of now I don't have access to good films for that (Bergger Printfilm is out of stock, and also the cost of that would add up over time). I also know I could make digital negatives, but I'd like to keep my process completely analog.
So, over the past few months, I've been working on ways to enlarge salt prints, and I think I'm getting close to a working process.
My first attempt was to build a UV head for my enlarger, long story short, it wasn't nearly bright enough standard salt prints. For a while I worked on designing an extremely powerful ~400 to ~600 watt condenser head for UV light, and I did finish designing it, but it would be very expensive to build, in large part due to the big water cooling loop which would be required to keep the LEDs from over heating.
That forced me to take a break in my search for enlargeable salt prints. The breakthrough I had which got me working on this again came while I was reading Jonathan Hilty's autochrome guide. I was reading the section about sensitizing the halides to get faster exposures, and realized that I may not be able to easily or affordably build an enlarger for printing traditional salt prints, but there shouldn't be a reason why I can't use more modern techniques to sensitize the process to visible light.
The first thing I did for this was to replace the sodium chloride salt usually used for salt prints out for ammonium bromide. From what I've read, silver bromides have a higher sensitivity range than silver chlorides, so using ammonium bromide increases the sensitivity of the paper to around 425nm, just within the visible range. To make it faster, I first looked into using steigmann's solution, which contains very small amounts of sodium thiosulfate and gold chloride which adds defects to the silver halides making them more reactive. Steigmann's solution must be heated to around 55c to activate though, and I couldn't figure out a good way of doing that. I did try using a heat press, but mine turns on at more than 55c, and it seemed to fog the paper. Talking with Jonathan though, he recommended I look into dye sensitizers for my process, and that's what I've done.
As I mentioned earlier, silver bromides are sensitive up to around 425nm, and with the addition of erythrosine, a red dye, they become sensitive up to around 525nm, making the halides orthochromatic. This is what I've found to be most effective. After the paper has been salted with ammonium bromide and dried, I brush a solution of erythrosine on to it. I've been told erythrosine works best when present before the formation of the halides, so I coat the erythrosine prior to the silver nitrate. This will make the paper pink, but it will wash out at the end, so there's no need to worry about the final prints being pink. For my latest tests, I've been adding erythrosine in the amount of 100mg per mole of silver. I may bump that to 200 and see if it makes the process any faster. Then, after the erythrosine has dried, I coat the paper with 15% silver nitrate, and leave that to dry.
As it is, this paper will now work for visible light contact printing, exposure times would depend on what your light source is, but I think it would be similar to normal salt printing given a similarly powerful lamp. Just creating a visible sensitive contact printing paper wasn't my goal though, so I began using gallic acid as a developer for the salt prints. This was a technique developed by a 19th century frenchman named Blanquart-Evrard, and theres a good thread in this forum on using it for normal salt prints. After exposure of the paper under my enlarger (15 minutes was what I did for my latest test) I brush a 1.4% solution of gallic acid over the paper to develop the image further. From what I understand, gallic acid takes free silver in the paper, and builds up density in the exposed areas... I'm not sure exactly how it works, but that's the general principle I think. More silver nitrate can be added to the gallic acid solution to make it build density faster, but in my experience adding silver nitrate leaves the print with a mottled texture I don't like.
This print I made yesterday has good density in the shadows, but the highlights are a bit dirty. I'm not sure exactly why that is, I think my gallic acid may have been contaminated with some silver nitrate since I had been using it throughout the day prior to making this print.
The process to create this image was as follows: Float paper on a solution of 2% ammonium bromide and 0.2% gelatin. Once dry, coat with erythrosine solution so that the erythrosine measures 100mg per mole of silver in the silver nitrate which will be used. Then, under a safelight since the process is visible sensitive, coat with 15% silver nitrate. Expose under an enlarger until the image is faintly visible. Brush a 1.4% solution of gallic acid over the print so that it completely covers, and wait a few minutes, if there isn't enough density, brush more over it and wait some more. Keep doing that until you have the tones you want. Then, fix and wash as you would a normal salt print.
Here are some images of the process, the first is the finished print, the second is erythrosine coated paper, the third is the print exposing under my enlarger, and the 4th is the print in the fixer remover bath.
There's one issue for me with traditional alt processes though, and thats contact printing. I shoot 8x10, so contact printing is possible, but I love big prints. I'd like this series to be at least 16x20, and maybe even 30x40, but as the shots are landscapes mostly, hiking around with a 30x40 camera would be a bit challenging. I know making large internegs is possible, but as of now I don't have access to good films for that (Bergger Printfilm is out of stock, and also the cost of that would add up over time). I also know I could make digital negatives, but I'd like to keep my process completely analog.
So, over the past few months, I've been working on ways to enlarge salt prints, and I think I'm getting close to a working process.
My first attempt was to build a UV head for my enlarger, long story short, it wasn't nearly bright enough standard salt prints. For a while I worked on designing an extremely powerful ~400 to ~600 watt condenser head for UV light, and I did finish designing it, but it would be very expensive to build, in large part due to the big water cooling loop which would be required to keep the LEDs from over heating.
That forced me to take a break in my search for enlargeable salt prints. The breakthrough I had which got me working on this again came while I was reading Jonathan Hilty's autochrome guide. I was reading the section about sensitizing the halides to get faster exposures, and realized that I may not be able to easily or affordably build an enlarger for printing traditional salt prints, but there shouldn't be a reason why I can't use more modern techniques to sensitize the process to visible light.
The first thing I did for this was to replace the sodium chloride salt usually used for salt prints out for ammonium bromide. From what I've read, silver bromides have a higher sensitivity range than silver chlorides, so using ammonium bromide increases the sensitivity of the paper to around 425nm, just within the visible range. To make it faster, I first looked into using steigmann's solution, which contains very small amounts of sodium thiosulfate and gold chloride which adds defects to the silver halides making them more reactive. Steigmann's solution must be heated to around 55c to activate though, and I couldn't figure out a good way of doing that. I did try using a heat press, but mine turns on at more than 55c, and it seemed to fog the paper. Talking with Jonathan though, he recommended I look into dye sensitizers for my process, and that's what I've done.
As I mentioned earlier, silver bromides are sensitive up to around 425nm, and with the addition of erythrosine, a red dye, they become sensitive up to around 525nm, making the halides orthochromatic. This is what I've found to be most effective. After the paper has been salted with ammonium bromide and dried, I brush a solution of erythrosine on to it. I've been told erythrosine works best when present before the formation of the halides, so I coat the erythrosine prior to the silver nitrate. This will make the paper pink, but it will wash out at the end, so there's no need to worry about the final prints being pink. For my latest tests, I've been adding erythrosine in the amount of 100mg per mole of silver. I may bump that to 200 and see if it makes the process any faster. Then, after the erythrosine has dried, I coat the paper with 15% silver nitrate, and leave that to dry.
As it is, this paper will now work for visible light contact printing, exposure times would depend on what your light source is, but I think it would be similar to normal salt printing given a similarly powerful lamp. Just creating a visible sensitive contact printing paper wasn't my goal though, so I began using gallic acid as a developer for the salt prints. This was a technique developed by a 19th century frenchman named Blanquart-Evrard, and theres a good thread in this forum on using it for normal salt prints. After exposure of the paper under my enlarger (15 minutes was what I did for my latest test) I brush a 1.4% solution of gallic acid over the paper to develop the image further. From what I understand, gallic acid takes free silver in the paper, and builds up density in the exposed areas... I'm not sure exactly how it works, but that's the general principle I think. More silver nitrate can be added to the gallic acid solution to make it build density faster, but in my experience adding silver nitrate leaves the print with a mottled texture I don't like.
This print I made yesterday has good density in the shadows, but the highlights are a bit dirty. I'm not sure exactly why that is, I think my gallic acid may have been contaminated with some silver nitrate since I had been using it throughout the day prior to making this print.
The process to create this image was as follows: Float paper on a solution of 2% ammonium bromide and 0.2% gelatin. Once dry, coat with erythrosine solution so that the erythrosine measures 100mg per mole of silver in the silver nitrate which will be used. Then, under a safelight since the process is visible sensitive, coat with 15% silver nitrate. Expose under an enlarger until the image is faintly visible. Brush a 1.4% solution of gallic acid over the print so that it completely covers, and wait a few minutes, if there isn't enough density, brush more over it and wait some more. Keep doing that until you have the tones you want. Then, fix and wash as you would a normal salt print.
Here are some images of the process, the first is the finished print, the second is erythrosine coated paper, the third is the print exposing under my enlarger, and the 4th is the print in the fixer remover bath.
