Diluting gelatin with alcohols

Simon Moore <couteaufin [at] aol__com> writes

>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. ...

I wanted to add a few things to Mr. Moore's comments about gelatine
glues, commonly known as hide glue to woodworkers. There is a system
to measure strength of hide/gelatine glues: it is easy to research:
it's called gram strength. The higher the gram strength the faster
the glue gels and sets, before drying. Common gram strengths are
between 180 and 350, 350 meaning it will gel quite fast. A quick
Internet search on 'hide glue gram strength' will provide a few
reliable product websites and essays which explain how it works.

One has to be careful about using it to glue older layers of hide
glue to glass because the fresh glue can grab the leaves of older
material and pull them away from the substrate when a high gram
strength glue is used. There is a variable amount of shrinkage which
happens right away as the glue gels. Testing is advisable before
carrying out final work. The proteins break down at around 148 deg.
F.  As long as the temperature stays below that, reheating several
time is not a problem. Also often the addition of other elements to
hide glue can change the rate at which it dries and can sometimes
make it "creep" over time. Salts and urea not recommended as
extenders to the open working time as the glue may not ever fully
dry.

Stephen Faulk
Guitar Maker/Restorer


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                  Conservation DistList Instance 26:6
                   Distributed: Monday, July 2, 2012
                        Message Id: cdl-26-6-003
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