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Butvar® B-76 is a thermoplastic, polyvinyl butyral resin. Butvar® B-76 is supplied in coarse powder form with an unlimited shelf life, which dissolves (albeit slowly) in a solution of either acetone or ethanol (amongst others). It sets when the solvent evaporates. It is mostly used nowadays in fossil preparation as a consolidant, a semi-matt varnish, a translucent but strong filler material and less commonly as an adhesive.
Butvar B-76 as a filler material in fossil preparation: It can be combined with ground matrix to create a natural filler paste, which is rigid when set but easily dissolved or reworked.
It is often best used as a field consolidant or mid-mechanical prep consolidant as it is easier to remove than Paraloid B-72. Butvar B-76 redissolves in acetone or ethanol much more readily than Paraloid B-72 if used as only a temporary consolidant. The matrix isn't consolidated quite as firmly and adhesion with the specimen isn't as strong as with Paraloid B-72. This has it's advantages when working mid prep - the matrix can be consolidated for mechanical removal with an air scribe, but isn't too firmly set.
If using as a varnish, Butvar B-76 has a more matt (much less shiny) appearance than Paraloid B-72 which is often desirable. In this sense, it is similar to Mowithal B30H.
It also has a higher glass transition temperature (62-72C) than Paraloid B-72, making it better suited to fieldwork in hotter climates or storage of specimens in warmer rooms (glass roof, conservatories, etc.).
Soluble in acetone, ethanol, xylene, toluene and more. For instructions of how to mix Butvar B-76 effectively check out our article on mixing Paraloid B-72. Whilst you might need to play around with the concentrations depending on your application, the principles of measuring and mixing are the same. Butvar B-76, however, may take longer to dissolve than you expect. The process can take several days.
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