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<p>[QUOTE=&quot;calcol, post: 24858467, member: 77639&quot;]First, it’s a neat project; I like it.&nbsp; However, rate of diffusion of gases through solids depends on more than molecular size.&nbsp; For example, both oxygen and carbon dioxide diffuse more rapidly through shellac than water vapor even though they are bigger molecules than water (see ref below). One thing, which is probably not a factor here, is whether the gas reacts chemically with the solid.&nbsp; Another thing is whether the gas is attracted or repelled by charge or polarity to the solid molecules but does not react to form a new compound.&nbsp; Even more complex, the microscopic of arrangement of molecules in the solid, things like crystals and channels, can affect the diffusion of specific molecules.&nbsp; I have no idea whether volatiles from the wood in your cabinet would penetrate shellac faster than water vapor.&nbsp; Likewise regarding diffusion through other coatings like urethane.&nbsp; However, volatiles will penetrate shellac much slower than through air.</p><p><br /></p><p>Cal</p><p><br /></p><p>Permeability of Shellac Coatings to Gases and Water Vapor. J Ag Food Chem 39:824, 1991.&nbsp; This article must be read carefully because, irritatingly, different units were used for water vapor versus other gases.&nbsp; According to the article, as a water vapor barrier, shellac is better than cellophane or nylon but not as good as polyester, polyethylene, or polypropylene.&nbsp; And for oxygen and carbon dioxide, shellac is a better barrier than cellulose acetate, polyethylene, polypropylene, polycarbonate or polystyrene but not as good as nylon or polyester.&nbsp; Alcohol-based shellacs were better than water-based shellacs.&nbsp; Bottom line:&nbsp; shellac is just fine to use.[/QUOTE]</p><p><br /></p>

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