Rejuvenating a "viable shellac finish"

[Schatznut]

Following my recent success in refinishing a Juba tambour clock whose shellac finish was coming off in big chunks, I bought an early 1950's Junghans tambour which, from the pictures, appeared to have a badly damaged finish, so that I could get further practice redoing shellac finishes. But when I got it and looked it over, it actually is in quite good condition - it has some minor crazing here and there but the finish is intact and the wood is undamaged. Mindful of Craig's admonishment in his excellent shellac tutorial (" I'd like to caveat this discussion by saying that I don't under most circumstances recommend applying new shellac to an old case that has a viable finish on it."), I'd like to have a go at rejuvenating the existing finish. But...after dropping that little bomb, he offers no direction whatsoever about how to go about it. So rather than messing it up, I'd like to hear from others that have had success bringing an existing shellac finish back to life before I just dive in. What has your experience taught you?

Thanks for any and all constructive suggestions (after all, this is the "Case Construction and Restoration" board).

 

[svenedin]

I am not an expert on this by any means but I have successfully revived shellac finishes (and I also watched a professional French Polisher do this to an antique bookcase of mine). Stage one is to remove dust and dirt. Remove surface dust with a soft cloth (basic dusting) and blow off with canned air. Then examine the finish and see how dirty it is. You could simply stop here if you wish. If dirty with grease from handling or smoke from open fires/tobacco and old dirty wax polishes then use a solvent that will remove the greasy marks but not dissolve shellac e.g. turpentine/turpentine substitute (white spirit) on a very fine abrasive pad or 0000 steel wool. You may wish to be very conservative with the cleaning to leave a more aged appearance and stop here. If the shellac finish is lightly cracked or crazed you can then wipe over with a lint free cloth very lightly moistened with alcohol and a little extra French Polish. This will dissolve the top layer of shellac and smooth out the cracks (you cannot do this to a surface that is dirty or dusty or you will simply embed the muck/dust in the softened shellac). I would call this process "rejuvenating" as it does not involve stripping to bare wood but even so it may be too much for those who like their clocks to show their age and history. One other tip: beware pieces that have had modern spray polish used on them. These contain silicones which will "fish eye" shellac finishes if not removed first.

Lot of good advice here: Tips and Advice () | Liberon wood cares and products

 

[Schatznut]

Thank you for the information and advice! After removing the trim and chapter ring, I'm less confident of the possibility of saving the finish, but I'm going to give it a go because there's nothing to lose by trying - if I'm not successful, it will need to be stripped and replaced anyway. Interestingly, the front surface has (had) a high-gloss french polished finish whereas the top surface has a conventional finish with the grain marks visible. This is not due to weathering or aging of the finish. Not in a position to post photos now but will try to get a few before I start in on it.

And thank you for the link to the Liberon site.

 

[Schatznut]

I've had some time to experiment with the Junghans tambour case and will share some of the early work. This case is kind of odd in that the top surface finish still looks almost perfect at 70 years of age but the front face has heavy crazing. The top looks like it has a few coats of shellac, whereas the front looks much more like it had a lot more coats on it initially. The area that was covered by the chapter ring shows only light striations along the grain of the wood.

I'll polish the top a bit but I will restrain myself from doing any major surgery - it just does not need it:


But the front face finish is heavily crazed:


I experimented with the front inside the chapter ring. I cleaned it with mineral spirits and allowed it to dry. Then I floated on some alcohol using my mop brush to reflow the surface of the shellac and allowed it to dry. I did this three or four times. Once it was thoroughly dry, I leveled it with 0000 steel wool lubricated with mineral oil. Then I cut it back using plain old car paint polish and a microfiber towel. The polish I'm using is pure white, and the residue on the towel from the polishing operation had a slight orange tint from the shellac. Polishing took some time and elbow grease but the finish came up nicely. Finally, I gave it a coat of Renaissance wax. Here's how it came out. The striations seen in the finish are following the grain of the wood (it's very nicely bookended at the center of the dial area). The crazing that was so prominent initially is almost imperceptible now:


If I can succeed in getting the rest of the front to look as nice as it has come out inside the chapter ring without causing any damage to the existing top surface finish where it meets the front, I'm going to consider it a success and stop. If something goes sideways or doesn't look right when I get done, I'll strip it and start over. But my goal here is to restore and preserve the original finish instead of replacing it.

In the meantime, the movement, which I've already overhauled, is ticking away happily on a test stand on the bench, taunting me every half hour...

 

[MartinM]

I'm quite impressed by your progress on this project. I rarely deal in rejuvenation of wood finishes but, might be emboldened to try my hand at breaking down the roughness and giving new life to a finish that the crypt keeper enjoys.
My attempts at this, to date, usually mean stripping back the finish and color to something that looks nothing like natural wood.

 

[JimmyOz]

I doubt this case was shellac to start with, the mass production of this type of clock would have needed an army of French Polishers to keep up.
Also you said you floated alcohol a few times over the surface, that would have melted the shellac into an uneven mess.
My guess it was some sort of Varnish sprayed on.
That said, I am all for experimenting and widening skill levels and if shellac works and it looks good no problem.