From: Sandy King (sanking@CLEMSON.EDU)
Date: 04/08/02-08:01:56 AM Z
Philippe wrote:
>Witho,
>
>
>>I have two questions concerning the coating of gelatin on papers.
>>First : Last night I tried to coat Rives BFk with a 5% gelatin/ 1%
>>aluminiumpotassiumsulfate solution. I coated the papers with a hake brush.
>>The paper should be used for carbon double transfer or, after some extra
>>coats, as an oilpaper. Very tiny bubbles now show as little shiny specks.
>>Will these specks harm the final print ? or should I use those papers just
>>for tests ? Is there a remedy against these specks or bubbles ?
>
>I had similar results when I tried to size some papers w/ different
>gelatins or colloids. These little shiny specks are not bublles, but I
>am pretty sure (99 %) that they are actual gelatin microcrystals. Their
>crystalline faces reflect the light and give shiny specks. I don't
>remember who told me this and how to avoid that neither. If I don't
>forget, I will check in my gelatin science handbook.
First, let us assume that Witho does have a problem with bubbles,
which is quite likely since the method of sizing he describes does
lead to the formation of many tiny bubbles. Bubbles tend to form as
the solution cools and when the paper dries they leave specks. The
solution to this is to mist the paper lightly with alcohol just after
brushing, and before the gelatin solution begins to set. This will
eliminate virtually all bubbles. You might also try a slightly more
dilute gelatin solution, say 2-3% and this will delay set time
somewhat and give you plenty of time to mist.
If the problem is due to the crystalline faces of the gelatin
microcrystals a solution might be to add some starch to the gelatin
solution to give a more matte surface.
Sandy king
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