French polishing

[David Houchens]

I have been playing around with padding some spirit varnish(shellac,alcohol,alittle oil). I've heard that adding small amounts of sandarac will make it softer or more flexible. How would this effect curing(slower maybe) and would it effect the way it pads on? Would you use this on the last coat as well? Thanks David

[testore]

sandarac is a harder resin. mastic will make it softer.I add both to my spirit varnish. Use less mastic than sandarac.

[amowry]

I use both in equal quantities by weight, and yes on the final coat as well. I'm actually not sure if it affects how it pads, because this is all I've ever used, but I've wondered about that. I used to add some lavender spike oil, which smelled great, but I think that may have affected the way it padded. If you are brushing it on the oil may be a good idea because it slows the drying time. The mix seem to be plenty flexible, as I've never been able to make it cold check. Sandarac tends to add a distincitve shine, which some people don't like.

[MarkG]

In my experience using sandarac in a spirit varnish can cause scratches in the finish to be more visible, especially when used over a dark stain. The sandarac seems to cause the scratches to be much more white and powdery in apearance. Sandrac (at least the stuff I've used) seems to form a light dusty powder when crushed which is something I've not observed with mastic. The spirit varnishes I've used with mastic but no sandarac don't seem to have the same scratching issues.

Has anybody else observed anything similar?

[David Houchens]

Oh well, 180 degrees off again. Is ths mastic, gum mastic? What ratio to the amount of shellac flakes do you use. Does this slow down curing time? Do you use UV lights to dry? Sorry so many questions at once. Thanks to all, David

[Bernie Daniel]

testore: sandarac is a harder resin. mastic will make it softer.

By "mastic" I assume you are referring to the same plant resin from Greece that is used to make chewing gum, as a setting agent in desserts and a filler in tooth pastes? #

Very interesting. #Where do you obtain your supplies of mastic and sandarac? #Thanks much!

[Michael Lewis]

Obtain supplies from Kremer Pigments, Int'l. Violin, Howard Core Co. etc.

[amowry]

Yep, it's gum mastic, and I get mine from Kremer. It's not cheap. but a little lasts a long time. I use about 5 grams each of mastic and sandarac with about 45 grams of shellac (it's basically the 1704 recipe that you'll find on the web). Interesting about sandarac showing scratches more, Mark. I haven't experimented enough to know. The stuff I use definitely forms a white powder, though-- I grind it in a coffee grinder, and there's usually a cloud of it in the air. Nothing smells better than a cloud of shellac, sandarac, and mastic (I'm serious)!

[MarkG]

Yes, it's gum mastic. The attached image shows gum sandarac on the left and gum mastic on the right, as you can see the sandarac does look a bit more powdery then the mastic. My thinking is that finish which contains sandarac generates this dust when it scratches which makes the scratches more visible. I'd love to know if anyone else has experienced this. Both of these were purchased from Hammerl in Germany I believe than International Violin distributes the Hammerl products in North America. You shold also be able to get them from most good distributors of artists materials.

I currently add about 15g of mastic to 100g of shellac. I like to think that this creates a more flexible film than using shellac on it's own, but this is pure speculation on my behalf. There are plenty of builders using spirit varnishes containing just alcohol and shellac and they seem to be doing just fine (Steve Gilchrist is one that comes to mind). But then again, formulating your own finishes is fun, and Andrew's right - it does smell amazing!

[buddyellis]

I love Gum Benzoin. I add a small amount of it to my shellac and paint my end blocks with it (just for the smell, on the end block). 50gr button and 5 gr of benzoin to ~~500ml spirit. Its probably a good idea to add some sort of UV inhibitor, too such as some of the stuff from Tinuvin.

[testore]

I got mine while in Greece years ago. It's crazy expensive everywhere BUT Greece. It apparently washes up on the beaches on the islands. I bought about a pound for 6 dollars in 1990.That same amount then would have run over 100 dollars from a supplier. you can buy mastica ice cream on every corner in Greece.

[jasonharsh]

I like to add a little manilla copal a.k.a. gum copal to my shellac. It makes it a little more glossy and a little more flexible without being much softer.
If you add one ingredient (mastic) to make it softer, and one (sandarac) to make it harder, are they just counteracting each others affect on the finish or is there something else at work there? Or is just because thats whats in the recipe of 1704?

Just Curious http://www.mandolincafe.net/iB_html/non-cgi/emoticons/rock.gif

Jason

www.highlandstrings.com