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Hand Rubbed Sunburst Finish.

PostPosted: Sat Sep 16, 2017 4:10 pm
by Gilbert Fredrickson
Should I apply a hearty washcoat of shellac then apply color? Should I mix the color in1# shellac or straight alcohol?

I think I may be finished with spraying lacquer. Thank you.

Re: Hand Rubbed Sunburst Finish.

PostPosted: Sun Sep 17, 2017 5:30 pm
by Alan Carruth
Normally I think the color coats come early in the process; that way the clear coats protect the color, and give you something to polish without cutting into the color coats.

There are several ways to do the color coats for a hand rubbbed burst. One is to apply dye or some other color dirctly to the wood, and use solvent to wipe it back to shade in. The color penetrates the end grain parts of the wood, which acentuates curl, but also locks it in: the dark stripes stay put as you move the wood around. This seems to be the standard method with arch back mandos, and possibly other types of instrumments. There was a nice article on this in 'American Lutherie' a couple of years ago.

Violin makers would typicaly apply some sort of clear seal coat and put color over that. The sealer or 'ground coat' could be anything from a wash of shellac through a French polish type pumice fill to several coats of spirit or oil varnish. The importasnt thing is to fill the end grain with a clear coat so that it won't absorb too much color. Often the sealer will have, or be followed by, a coat of something with a different color from the final coat. Yellow, such as you'll get from gamboge resin, is common. This helps give a 'dichroic' effect, where the color of the finish looks different from different angles. The object here is to get as even color and as smooth a surface as possible, without too much build. If you're using an oil varnish you'd sand back almost to the wood at this point.

Shading is often done by wiping, in a manner similar to the way dyes are used on bare wood. This works particularly well with oil varnishes, which are hard to feather out at the edges. You would apply a color coat around the edges where you want it to be dark, and wait a bit for the varnish to start to gel. Then use a rag with some thinner to wipe the edge back and feather it out. Once the first color coat is dry you sand it lightly and apply another, covering a larger area.

Violin makers also often use glazes of oil paint colors. For this it's normal to use a 'lakes' type pigment; dye that has been captured in a transparent almina precipitate. Often paint straight from the tube can be wiped on in a very thin layer, and allowed to dry before the next coat of varnish is applied. The goal on violins is usually to mimic wear patterns and age, and colors such as ocher, umber, and burnt Siennna are used to get the look of dirt or aged varnish in some cases.

Shading with lacquer is usually a spray technique (although you can wipe shade if you want), and this can also be done with shellac and some oil varnishes. Some makers use small air brushes for this. It's pretty much the same method as with varnish, except that it's easier to feather the edges, so you don't need to wipe back.

As I say, however you do the shading it's pretty normal to follow up with at least a few clear coats. Keep in mind that even a fairly thick finish won't usually be more than a few thousandths of an inch thick, and if you start to rub into the color coats as you polish up you can end up with lighter spots.

Re: Hand Rubbed Sunburst Finish.

PostPosted: Mon Sep 18, 2017 8:54 am
by Arnt Rian
Alan covered a lot, I'll just add that its not just the "3D-effect" that is different if you rub the colors directly onto the bare wood. The colors will also be more uneven, and there is a bigger chance for blotches and mistakes that are difficult to repair when you do this. However, when done well, the hand rubbed method to me tends to look more lively and interesting; a burst sprayed over a clear coat is usually more even and predictable, the rubbed one looks more 'hand made'.

It is also quite common us combine the methods, one of the difficulties with rubbing is to get the accents dark enough. One method is to rub the base colors, add a clear coat, and when you see the result of this, add darker colors to taste around the the perimeter with a spray gun, before more clear coats. Etcetera.

Another thing to remember with colors wiped directly on the bare wood, is that different woods 'take' the colors quite differently. Spruce and maple will need different amounts of solvent to blend well and avoid blotches. Arch top instruments, which have varying degrees of end grain because of the geometry of the top, can be a challenge because of this.

Re: Hand Rubbed Sunburst Finish.

PostPosted: Fri Sep 22, 2017 10:21 am
by Steve Sawyer
There was an article on hand-rubbed sunbursts by James Condino in American Lutherie #125 (Spring 2016)

Re: Hand Rubbed Sunburst Finish.

PostPosted: Fri Sep 22, 2017 1:32 pm
by Bob Francis
Steve Sawyer wrote:There was an article on hand-rubbed sunbursts by James Condino in American Lutherie #125 (Spring 2016)

There is a video by Condino delivers a lot of information in a short period of time. I think it is a Fine Woodworking video.

Re: Hand Rubbed Sunburst Finish.

PostPosted: Tue Sep 26, 2017 12:02 am
by Jason Rodgers
Bob Francis wrote:
Steve Sawyer wrote:There was an article on hand-rubbed sunbursts by James Condino in American Lutherie #125 (Spring 2016)

There is a video by Condino delivers a lot of information in a short period of time. I think it is a Fine Woodworking video.

Sure am glad you mentioned the video. I read that article and was disappointed I missed that session at the GAL conference.