Re: Gum variables

Sam Wang (stwang@CLEMSON.EDU)
Thu, 11 Jun 1998 22:25:11 -0400

Suzanne,

Aha! Here's someone who did her homework!

I guess it is timely to revise or at least clarify my numbers. In trying to
respond to Judy's questioning of both the method and the amount of
dichromate that I use, I carefully weighed it: I use .25 gram (that's a
quarter of a gram) of ammonium dichromate in each 10 cc of working gum
solution (I dilute the gum with equal parts of water first, add pigment,
then add the powder dichromate). So, the dichromate concentration is .25
divided by 10 = .025, or 2.5%.

In his Keepers of Light, William Crawford said to use 35.7 grams of
ammonium dichromate in 64.3 ml of water for making the sensitizer. When
equal amounts of sensitizer and gum are mixed together to make a working
solution, this makes the dichromate concentration 27.76%:

35.7/(2X64.3)=.27760497667

So, the question I have is: if 2.5% gives me plenty of printing speed, why
in the world do people still insist on using 10 times that amount, and
dumping it down their drains!? (BTW, this is not a flame, OK?)

Or am I missing something here?

Thank you Suzanne for bring that up.

Sam

>Exactly 3 years to the day before Sam Wang's latest message (Jun-10-1995),
>he wrote to the list, "I use 2% dichromate (either ammonium or
>potassium) for gum. . ." I was just beginning to think about trying
>gum and being Scotch, using the least amount of chemical seemed the
>way to go. I haven't compared using different dilutions and since I
>print outside, times aren't very meaningful (3-10 minutes depending on
>sun/clouds). I use about equal volume of gum and dichromate solution.
>As Sam said in '95, using less dichromate means less gets put down the
>drain and you're spending less. It works for me and I am happy with
>the results I am getting.
>
>Suzanne Izzo s_izzo@guvax.georgetown.edu