Diluting gelatin with alcohols

Cheryl Jackson <cheryl.jackson [at] naa__gov__au> writes

>I have been trying to dilute a 10% W/V aqueous solution of gelatine
>with ethanol or isopropyl alcohol (down to 2%) without success. It
>keeps turning stringy and opaque.
>
>Should I be using a different grade of gelatine?
>
>The solution will be used to consolidate a flaking gelatine emulsion
>back down onto its glass plate.

The problem of using alcohol with gelatine is that the protein
chains are coagulated by the alcohol, hence the white strings.  Just
hydrate the gelatin in a little warm water, if it's too viscous you
can dilute it further by adding more warm water.  It is difficult to
'thicken up' if too dilute and constant re-heating damages the long
molecular chains in the gelatine.  Use leaf gelatine rather than
powder, it has better adhesion for some reason. If you do this type
of work regularly it is worth making up a batch of hydrated gelatin
by adding 1 ml of glacial acetic acid in the gelatine mix and 2ml of
glycerol (per 100 ml) to your hydrated leaves of gelatine.  Warm
this and mix these into the mixture; pour out the resulting viscous
solution onto a glass plate to solidify.  It can then be cut up and
stored.  It is used by melting in a double beaker--(beaker in a
larger beaker of hot water) like a bain-marie.  Store the hydrated
gelatine in an airtight jar.  The glycerol will prevent it from
drying out too quickly (humectant) and the acetic acid acts as a
fungicide and help bind the gelatine more strongly to the glass
(somehow!).

Simon Moore MIScT, FLS, ACR,
Conservator of Natural Sciences and Cutlery Historian


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                  Conservation DistList Instance 26:5
                  Distributed: Saturday, June 23, 2012
                        Message Id: cdl-26-5-001
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