Glad to hear from you. I was at Berindo for three days working on a project. It was very pleasant to work with them, and there is always something amazes me at Benrido.
Thank you for your information. This gives me something to start with. I am trying to see if w can try different kind or concentration to expand the tonal range.
They can do (and do it all the time) something similar at the printing stage, but I am interested in coming up with a plate so that it will be a little more efficient. I am just trying to figure out how to do a series of test this this fall before I go back to Japan.
I will be back in Kyoto again in December. If you have time, maybe we can meet in person in Kyoto.
On Sep 22, 2009, at 9:50 PM, geoff chaplin wrote:
I don’t know if anyone replied to your posting – I didn’t see anything on the list. I too went to Benrido and was intrigued to hear they used a Pot / Amm Dichromate mix. I have no experience of the collotypye process myself but I can tell you my experience of different dichromate mixes with gum and PVAL. The higher the concentration of dichromate the shorter the printing time – it seems to go roughly in proportion – 10% dichromate is twice as fast as 5%; 20% is 4x as fast. Of course you can only go to about 13% with Potassium but 27% (?) with Ammonium dichromate. Other than the strength I know of no difference between Pot and Amm. One other impact of changing the strength of the dichromate is the tonal range that prints. This is also affected to a lesser extent by the light source and also by the pigment being used. Using PVAL and 5% dichromate I find a narrow tonal range gets printed. This is useful with B&W prints because it allows – by changing the exposure time – me to print different blocks of tones in different colours or shades. 13% dichromate and gum is generally sufficient to print a wide range of tones – more than 10 stops on the negative – so I rarely bother with stronger Ammonium. UK
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I am interested in knowing the difference of a tonal rage by using ammonium and potassium dichromate. It seems to be that ammonium dichromate produces a longer tonal range than potassium dichromate, say, in gum printing. Also, dilution of dichromate also affects the contrast rage, say, in carbon printing. So the kind and dilution affects the contrast range. I was in Kyoto for a last couple of days working with Benrido, who makes collotype prints. There were a few technical points that interested me. It seems to me that there is a room for an improvement. One of them is the use of dichromate and the dilution of it when they I was told that they mix gelatin and both potassium and ammonium dichromate at a certain dilution to pour on to 1/2" plate of glass. Also, they told me that they have not changed the way they make plates for a long time. The company has been around since late 1800's. As you can see in the video clip on Youtube, collotype is not purely chemicals process, and they are many variables during the process especially at printing stage. Once the plate is ready, a printer quickly assesses the condition of the plate based on their experience to determine how hard and how much of ink they use, including relative humidity and "wetness" of the plates. All these factors affect the So, I am interested to know if possible to gain a wider tonal range by changing the way they prepare the gelatin solution. Also, are there other effects we can see if they were to change the formula i.e. speed. Why people prefers one over the other in a given process in the Any suggestions and insights would be appreciated.