Re: gum top coat


Kevin O'Brien (kob@paradise.net.nz)
Wed, 14 Apr 1999 11:18:46 +1200


Aqueous acrylic emulsons are typically alkaline using ammonia. There are
dozens of acylic and other co-polymers used in the coatings industry and
there is no gurantee that Liquitex will be formulated the same from year to
year. It would be surprising if it hadn't changed from time to time.

Acrylics polymers don't behave like oil films which oxidise and harden,
turning yellow as they go. The polymerisation or most of it has already
taken place and whether it is aqeous or solvent based what is being used is
a finished acrylic or other polymer resin. The aqueous ones also have
solvents for the resin. The water evaporates first then the solvents assist
an even film to form as they in turn evaporate. A typical emulsion will also
have along with the resin, film forming solvents such as carbitols,
plasticers, ammonia, anti-foaming agents, levelling (brushing) agents and
possibly thickening agents.; pigments and sheen control are extras. The
chemistry varies amongst the different products so they are not always
mixable.

The argument could be made that the formula should be stated for fine arts
products.

> Doesn't Krylon yellow with age? or have a deleterious acid in it? I use
it
> with my pastels, but only out of desperation. For gum, I suggest a final
> varnish of Liquitex.
> Laura
>



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