From: Joe Smigiel (jsmigiel@KVCC.EDU)
Date: 04/06/02-07:15:05 AM Z
Hi David,
Two things pop out at me from the tale. First, you are using ammonium dichromate. Try some of the potassium salt if you have it. (I believe it stains less)
Second, you state twice you gave an hour's exposure (1 minute to 1 hour). Is the emulsion from the 1 minute exposure on the same sheet and/or has it been sitting around for an hour or more between the time you coat and process? There is a "dark effect" with gum dichromate emulsions that causes them to harden over time regardless of any exposure given. So, try shorter exposures with as little time between coating, drying, exposing and processing as you can. I use a hair dryer (no heat setting) to quickly dry the emulsion in a couple minutes tops and my usual exposures run between 1 1/2 minutes in sunlight to 3 minutes in a UV box or maybe 10 minutes with a 500w quartz light 6 feet from the paper. The exposed prints hit the water within a minute or two of exposure and clear within 30 minutes.
Joe
<<< nashcom@btinternet.com 4/ 6 4:59a >>>
Hi
I managed to get some time at Easter to have a bash at gum printing. I had made
some of the chemicals up at Christmas using the formulae in Scopick's book.
I soaked and dried the paper, then brushed on a gelatin/formaldahyde mix and let that
dry.
I mixed 2g of yellow, red and blue pigments (separately) with 10ml of gum.
I then mixed 2ml of the yellow pigment solution with 2ml ammonium dichromate, and
coated this on the paper in dim light, and let it dry in the dark.
I made various test exposures between 1 minute and 1 hour, then soaked the paper in a
number of still water baths. However, there was only the faintest of images, and the
paper didn't clear - the image area stayed a mustard yellow.
I had a think about this, then decided to dilute the pigment solutions. I did a number of
tests by adding an increasing amount of gum to 2 drops of pigment, and brushing onto
some prepared paper then soaking in water to see at what strength the paper cleared.
The yellow started to clear to a magnolia colour at about 2 drops pigment solution to 6
drops additional gum, and going as far as 20 drops gum didn't seem to make much
difference.
I then had another bash at 1 hour exposure, and got a faint image, but the paper still
didn't clear properly.
I had been expecting this process to be quite easy (I thought I might be blessed with
some beginner's luck!), and had been planning on making a tri-colour image. I had a go
with making 3 in-camera exposures with tri-colour red, blue and green filters, and
printing with yellow, magenta, cyan pigments, but I only got a faint image with a muddy
brown background.
By the way, I shot the images on Tri-X rated at 100ISO and developed in Rollo Pyro for
about 4 minutes (about half the time I normally use for platinum).
Any help would be much appreciated.
David Nash
This archive was generated by hypermail 2b30 : 05/01/02-11:43:29 AM Z CST