Re: Mylar as base for carbon tissue

Bas van Velzen (eland@knoware.nl)
Mon, 22 Apr 1996 09:08:44 +0100

>Also, I'm not sure, but it seemed that adding more sugar made the coating more
>brittle. Without sugar the gelatin layer had a consistency much like a thin
>layer of plastic, and was quite pliable. It was hard to say for sure if the
>coating with double the sugar was more brittle than that with the normal
>amount,
>but I had the feeling it was. More tests are in order, but it seems that the
>best combination may be the one with the minimum amount of sugar to keep the
>drying even.
>
>- Wayde Allen

When sugar is added to -glue-like substances to change its characteristics
one thing happens: the glue becomes more soluble in water. In, for
instance, some reversible PVA glues sugar is added to make it more soluble
and thus reversible (??). This will change the performance of the glue
(PVA) rather dramatically. Also the risk of mould or bacteria infections
becomes larger since sugar is a preferred substrate for many
micro-organisms (up to about 50% solutions, remember jams &c where sugar is
used as preservant).
Sugar dries to cristals and so mixed in with other materials it is likely
to make the resulting layer more cristalline -brittle-. Therefore
plasticizers like glycerine are added. The glycerine bonds water which will
result in a more supple layer since water acts as a lubricant.

Bas van Velzen

Jonge Eland papierrestauratie
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