Katharine Thayer wrote:
>
. This yellow stain, after being
> developed half an hour and dried, did turn brown when placed outdoors
> half covered; the yellow was completely replaced with tan/brown in less
> than an hour. While there was no direct sun, there was enough UV to
> create a brown dichromate stain within two minutes on a (separate) sheet
> of paper coated with dichromated gum, that I placed beside the other one
> for a rough test of the available UV.
>
It's worth, I think, making a special note of the fact that the
dichromate that's trapped in this yellow stain doesn't work as fast as
active dichromate in a gum-dichromate coating, as shown in the above
observation that it took an hour for the yellow dichromate stain to turn
brown in diffuse UV but only a minute or two for the gum-dichromate
coating to turn brown.
Katharine
Received on Thu Aug 11 12:05:19 2005
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