Re: First Carbon

On Mon, 16 Oct 2000, Joao Ribeiro wrote:

> up with a white paper after development.
> What went wrong?
> Tissue:
> 10% gelatin
> 1 % sugar
> 1 % sumi ink

This looks OK

> Final paper coated with 10 % gelatin unhardened

This also looks OK

> Sensitizer: 3 minutes at a 3% K dichromate solution

Good

> Dry

Yep

> Exposure: 6 minutes under a 400w Mercury Vapor lamp

What kind of Mercury lamp are you using? I have a 125 W Mercury sun lamp
and exposure times are on the order of 45 minutes! Let's see, making the
unlikely assumption that we have similar power spectral densities for
these two sources and that we have similar source to print spacing (about
24 inches in my case), your source puts out 3.2 times more power than
mine. That means that your exposure should probably be something more
along the lines of 45/3.2 = 14 minutes.

Under exposure would also be consistent with the no image failure mode.

> The final paper was put in a 25 o C tray for 5 minutes, the exposed
> tissue
> was put in the tray with the
> paper and immediately pulled out.

Did you wash the exposed tissue in cold water for about 1 minute before
putting it into the tray with the final support paper? This wash step
removes the soluble dichromate, and softens the gelatin layer.

> I removed the excess of water and put the tissue/paper under a glass
> plate with a 5 l water gallon on top of it for 10 minutes.

Yes, good.

> After that, the tissue/paper was put in a tray of 45 o C water and
> ended up with a white paper and black hot water.

I assume that you never saw anything resembling an image as the tissue
developed out?

> Was the exposure too short?

Almost certainly! I'd suggest you try again with around 15 minutes of
exposure and see what happens. You could also try exposing using direct
sunlight. I find exposures to direct sunlight to be on the order of 2
minutes. That is a quick test to try. It would also help determine the
efficacy of your light source, the viability of your tissue, and give you
the experience of getting a carbon image.

> Should I let the exposed tissue absorb some water before putting it
> into contact with the paper?

You should wash the exposed tissue with several changes of cold water to
help remove the dichromate and soften the tissue before putting it into
contact with the paper. This wash should probably only be on the order of
1 minute.

- Wayde
  (wallen@lug.boulder.co.us)
Received on Mon Oct 16 08:54:35 2000