> Of course not -- polyester needs a special pre-treatment. Try microwax.
Microwax ... I'm not sure what that is? I recently tried mixing a very
dilute gelatin solution, and applying this to the plastic sheet. I
basically used the pre-treatment described in the Keepers of Light book
for the collotype plates, except that I didn't have any sodium silicate
or alum to add. I just coated the sheet with the dilute gelatin solution
and let it dry. A second coating of 7% gelatin adhered quite nicely.
As I recall, you were asking about this sometime back with respect to
coating Liquid Light on a sheet of plexiglass. That was before this test.
> It was fresher and the sugar made it dissolve more easily... But the sugar
> is bad for long-term archivality. Better to use a small amount of
> glycerine to enhance contrast.
I have wondered how sugar might affect the life span of the mix.
However, most tissue formulae make use of it, and often use both sugar
and glycerin. Some formulae include a tiny bit of Thymol, supposedly
this helps eliminate bubbles? If nothing else, I would suspect that the
Thymol would counter the poor keeping properties of the sugar?
I was sufficiently curious about the effect of the sugar in the gelatin
solution to try mixing several batches of 7% gelatin with varying amounts
of sugar (no sugar, 1 teaspoon/100ml, 2 teaspoons/100ml). The results
were interesting in that the sugar seemed to even out the drying stresses
that formed in the raw gelatin. I assume that this was partly due to the
sugar retaining the water longer. I also tend to think that the sugar
increases the brittleness of the gelatin since the raw layer was quite
flexible. I didn't think to test for solubility. Perhaps glycerin would
minimize the drying stresses, and not increase brittleness? Perhaps many
of the tissue formulae I've seen use a combination of sugar and glycerin
to optimize the tissue for solubility and flexibility?
- Wayde
(allen@boulder.nist.gov)