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Re: [BKARTS] PVA softens PVA



>If you find you've left your PVA brush out to dry unwashed, try sinking 
>it up to the top of the bristles in fresh PVA for a couple of hours, then
>wash as usual. For some reason the wet PVA softens the dry very well.

*****************************

This is likely to happen only because the initial PVA formula you have 
is water-reversible, in which case it is the water content in the PVA 
which is causing the softening-up to occur.   Otherwise, if the PVA is 
non-reversible, only solvents will soften the glue.  (Some PVAs have a 
slight degree of reversibility, enabling recent dryouts to be reversed 
with water, but once severely dried, only solvents will allow 
softening).

Solvents like Toluene and alcohol will dissolve dried PVA, whether or 
not the initial PVA was made to be water-reversible.  

10 year old "dried" brushes can be loosened up with solvents, and this 
can take days or even weeks, for a thorough cleaning, and will probably 
need several new washes of solvent for the action to work effectively.

Many of the modern brushes with natural bristles, available from the larger bookbinding suppliers, have inferior hairs.  The brushes often dry with the hairs sticking out every way except straight.  Moreover, the bristle structures of some brushes do not have the required flexibility for bookbinding.  Invariably, the hairs are far too long for comfortable use, and one has to either trim the brushes, or extend the ferrule further into the brush area.  Many of the good old copper and iron - ferruled bookbinding brushes are either unavailable today or extremely expensive.  

As a consequence, such long-term soaking of older brushes is entirely appropriate to invigorate the bristles and give them another decade or so of use.

David

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