The forming of this kind of sediment and sludge in dilute dichromate
solutions is normal. There will have been some change in the printing
qualities of the solution from when it was first mixed but not enough to
make much difference. A more important consideration is how much tissue has
been sensitized with the solution. With increased use the PH of the
dichromate solution increases, resulting in less sensitivity and more
contrast. If you want to keep using the same solution you can work out a
replenshing system to keep it at the same PH. With replenshing the solution
will last longer if you 1)strain it back into the bottle after every use
and 2) keep it refrigerated.
In my own work I prefer to sensitize with a very small amount of sensitizer
which I discard after use because I find that this gives me more consistent
results. If you soak the tissue first in cold water to flatten it out and
use a flat bottom tray, with no ribs or indentations, you can get by with
about 100ml of sensitizing solution for an 8X10" print.
Sandy King
>I finally got back to tinkering with carbon printing this week, and
>discovered that my 3% solution of potassium dichromate had coated the
>bottle with a brownish black sediment. Is this normal? I strained the
>solution through a coffee filter, and scrubbed the inside of the bottle to
>remove as much of the sludge as possible. A couple of sample prints made
>using the solution seemed to turn out OK, but I'm wondering how long I can
>expect this solution to last?
>
>- Wayde
> (wallen@boulder.nist.gov)