Is there such a thing as a truly clear oil based polyurethane? I know they yellow over time, but don't they also apply amber?
asked Jun 19, 2015 at 16:16
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2 Answers
There are lighter and darker oil-based polys (and other varnishes, not all oil-based varnishes contain polyurethane) but essentially all are various shades of yellow. This is inherent to the product because they're oil-based, that base oil is almost invariably slightly yellow. But also refer to the Note below.
Broadly speaking the clear finishes — sometimes referred to as "water clear" or "water white" — are either waterbase varnishes (very different to oil-based) or a type of solvent finish (i.e. lacquer).
Note: quite a bit of the colouring that oil-based varnishes provide to wood is not due to them being yellowish. Put simply the effect is similar to what happens when you dampen wood with mineral spirits, which immediately gives a "deeper" or "richer" tone despite mineral spirits being completely clear.
You can use a shellac which will not amber your piece. Shellac has a lot of the advantages of polyurethane.
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The only two tints I've ever seen shellac in are yellow and yellower. Of course, they were labeled "clear" and "amber."– DoresoomCommented Jun 21, 2015 at 23:37
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You can tint shellac: earthpigments.com/non-toxic-shellac Also, lots of folks who use shellac buy the 'powder' - which comes in various pale colors - from blonde to orangeish - to a sort of pallid purple. You mix your own by adding ethanol (denatured alcohol) and methanol (wood alcohol) to the powder. The 'cut' of shellac is simply the amount in pounds dissolved in alcohol - 5lb cut being standard. But generally too thick for many finishing operations so you need to dilute it even more... see shellac.net Commented Jun 22, 2015 at 15:16
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