U of S | Mailing List Archive | alt-photo-process-l | Re: Ammonium and Pottasium Dichromate

Re: Ammonium and Pottasium Dichromate

  • To: alt-photo-process-l@usask.ca
  • Subject: Re: Ammonium and Pottasium Dichromate
  • From: Tsuyoshi Ito <tito@projectbasho.org>
  • Date: Sat, 26 Sep 2009 08:58:03 -0400
  • Comments: alt-photo-process mailing list
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  • Reply-to: alt-photo-process-l@usask.ca

Hi Geoff,

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:

Hello again Tsuyoshi,
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.
Hope that helps
Geoff Chaplin
 ジェフ チャップリン
Skype: geoffchaplin1611
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-----Original Message-----
From: Tsuyoshi Ito [mailto:tito@projectbasho.org] 
Sent: 10 September 2009 08:04
To: alt-photo-process-l@usask.ca
Subject: Ammonium and Pottasium Dichromate
Hi everyone,
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 
prepare plates.
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 
tonal range a quite bit.
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 
first place?
Any suggestions and insights would be appreciated.