From: Philippe Monnoyer (monnoyer@imec.be)
Date: 04/08/02-09:51:53 AM Z
Indeed, in emulsion making, alcohols are added to the emulsion itself to
avoid foam and bubbles. Amyl alcohol is sometimes used but ethanol works
well also.
Moreover, before coating films and papers, emulsion is de-gassed in
moderate vacuum to remove any bubble. This should be quite simple to set
up in one's darkroom with the compressor pump of an old fridge. This
works for a lot of things.
Something else : is a bubble speck shiny ? That's the word "shiny" that
made me immediately think of these gelatin crystals.
Cheers,
Philippe
Sandy King wrote:
>
> 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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