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Butvar® B-76 is a thermoplastic, polyvinyl butyral resin. Butvar® B-76 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.
It can be used as an alternative to Paraloid B-72 as a consolidant or varnish during the current lack of availability of Paraloid B-72. We recommend the 5% wt/vol solution for consolidation, which may need further thinning with pure acetone.
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. If you are familiar with Paraloid B-72, Butvar is much more viscous at 10% wt/vol and so will leave a thicker deposit.
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.).
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