Hello again Tsuyoshi,
I don$B!G(Bt know if anyone replied to your posting – I didn$B!G(Bt see anything
on the list.
I too went to Benrido and was intrigued to hear they used a Pot / Amm
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
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From: Tsuyoshi Ito [mailto:firstname.lastname@example.org]
Sent: 10 September 2009 08:04
Subject: Ammonium and Pottasium Dichromate
I am interested in knowing the difference of a tonal rage by
ammonium and potassium dichromate.
It seems to be that ammonium dichromate produces a longer tonal
than potassium dichromate, say, in gum printing. Also, dilution
dichromate also affects the contrast rage, say, in carbon printing.
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
One of them is the use of dichromate and the dilution of it when
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
Also, they told me that they have not changed the way they make
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
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
to determine how hard and how much of ink they use, including
humidity and "wetness" of the plates. All these factors
tonal range a quite bit.
So, I am interested to know if possible to gain a wider tonal range
changing the way they prepare the gelatin solution. Also, are
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
Any suggestions and insights would be appreciated.