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not getting exp. iridescence + depth with shellac French polish?

Posted by vladr (My Page) on
Sun, Jul 12, 09 at 12:47

I am preparing to coat about 20 pine shelves with Zensser Bull's eye amber Shellac.

Prior to starting the "big job", I sanded a plank of pine (220 grit), swiped both sides clean with a rag dipped in paint thinner, waited a few minutes, sealed the two sides with thinned down shellac (shellac + ethanol), then:

- On side #1 I applied two generous coats of shellac (within 5 minutes of each other) using a lint-free cotton rag
- On side #2 I applied about 8 thin coats of shellac over two days using a French Polish technique as described in http://www.milburnguitars.com/fpbannerframes.html and http://www.woodfinishsupply.com/GuideToFrenchPolishing.pdf

In the end both sides achieved the same tinting (nuance). Although side #2 (french polish) achieved a more uniform tint than piece #1 (two thick coats), piece #2 FAILED to achieve piece #1's depth and iridescence (mother-of-pearl-like effect) when examined in the light from different angles.

Essentially, side #2 looks fine, but it appears merely "stained" to the desired amber tint, whereas side #1 has that additional "lacquered" depth (that one can also get by dipping a small, previously sealed piece of wood in shellac then letting it dry.)

Why does side #1's shellac (two thick coats) look "deeper" than side #2 (8 thin coats with French polish)? Have I wrongfully assumed that the shellac has the same thickness on both sides when the same tint was achieved? Have the multiple FP coats fail to properly amalgamate on side #2 (did I not apply enough pressure? would this be a factor?)

Thanks,
Vlad.


Follow-Up Postings:

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RE: not getting exp. iridescence + depth with shellac French poli

I would have oiled the pine to pop the grain before shellac. I would have brushed on at least 4 coats of shellac to build a surface before beginning to pad on additional coats to get the full polish. Full curing time in between, too.
Softwood needs more ground coats than hardwood, because the grain needs more sealing. The oil (watco, what have you) is also needed on softwood to bring out the color and "texture" of the grain. Shellac just sits on the surface, after all.
I even oil some highly-figured hardwoods to get the pop before polishing.
Casey


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