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Re: Talking about adhesives



Shireen & Betty's questions are related so I will address them in common.

The earliest recipe using PVA in combination with methylcellulose that I'm
aware of was published in the conservation literature during the 1970's and
it was called 'Mix', a combination of 9 parts methylcellulose to 1 part PVA.

The advantages were that there was good open time for working, a thin dry
adhesive film, and if it became necessary to undo a repair, water would
take care of most of the problems, because 90% of the adhesive was water
soluble, leaving a 10% sticky residue to remove mechanically.

Paste (i.e., cooked wheat/rice starch paste) can be more troublesome to remove
than methylcellulose, but sometimes it is the right adhesive to add to the
combination (you decide when).

The reason PVA prevents mold (for a long time, but not forever) is because
it contains formaldehyde.  Other moldicides have been used, but generally,
when you open a container of PVA the main thing you smell is formaldehyde.

So, if you mix PVA with your paste the paste will also be protected.

I should probably mention that I don't use much PVA.  My current pint was
purchased in October, 1990 from Colophon, and the newest pint in storage
was purchased in February, 1996.  Nothing against PVA's; I just don't have
much need for them.

Jack


From:    Shireen Holman <tholman@CLARK.NET>
I have used PVA mixed with wheat paste. Is there a reason to prefer
methylcellulose?

Shireen

>From:    Betty Storz <storz@MCN.ORG>
>I've noticed that when I mix PVA with paste, the paste doesn't mold. Could
>it be that whatever preserves the PVA also keeps the paste from spoiling?

>Betty


Jack C. Thompson
Thompson Conservation Laboratory
7549 N. Fenwick
Portland, OR  97217

503/735-3942  (voice/fax)

http://www.teleport.com/~tcl

Bacteria is the only culture some people have.
        Anon.


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