It was impossible to find any info on this on the net, and since I have been working on it very hard for several months, and have it figured out, thought I'd post my experience.
I have been spraying lacquer on the hammered dulcimers that we build now for over 20 years. Figure I have finished at least 5,000 of them myself, so am pretty good with a spray gun. But lacquer is toxic, and even though I protect myself very well with a respirator, and complete HAZMAT suit, I still get a small dose. So I had been looking around for several years for a healthier alternative. Water based lacquer isn't feasible in my shop because it is temperature sensitive, and I can't maintain the warm environment year round. It is also a product of chemical companies, and works much the same as solvent based lacquers. But I finally found the right alternative... Shellac!
Shellac is old fashioned. It is what was used before lacquers came along over 100 years ago. It has some advantages over lacquer, but it is different, so needs to be handled differently. But once you learn how it works, I think you'll like it as much as I do.
One advantage is that it is totally nontoxic. Shellac is a natural material, produced by a bug that lives in India and Thailand. It is harvested by hand, and much of the processing is done by hand. It is edible, and you have eaten lots of it like in coatings on candy and medicine.
Shellac comes as flakes that you dissolve in denatured alcohol. I get my flakes from www.shellacshack.com. They come by the pound in several different colors and grades. Denatured alcohol is available at home centers, hardware stores, and paint stores by the gallon. Not all brands are the same, I use the Sunnyside brand, and it works well.
There is lots of stuff on the net about applying shellac by brush or pad, but none about spraying except to say that it is possible. So I had to do the experimenting myself. This is how it is done.
Use what is called a one pound cut. Which means dissolving one pound of shellac flakes in one gallon of alcohol. It takes a while for the flakes to totally dissolve. Just put them in the alcohol, and stir several times a day, and they will eventually completely dissolve. Use a glass jar for dissolving the flakes. It may take several days, be patient. Once they are dissolved, I filter the solution through a paint strainer into a clean plastic milk jug. Don't try to store shellac solution in metal containers, it is corrosive.
Shellac at a one pound cut can be sprayed through any gun that will spray lacquer. I am still using lacquer for some things, so I have a separate gun reserved for the shellac since the solvents are totally incompatible. Keep your gun clean! You want to make sure all the shellac solution is out of there before the end of the day. You can leave some alcohol in it, but no shellac.
Shellac can be sprayed directly on bare wood, but the alcohol being a polar solvent will raise the grain of some woods. Most of mine is sprayed on birch ply, so I need to seal the wood before spraying. I have found Minwax Wipe on Poly to be ideal for this. It can be used straight, or cut 50% with mineral spirits, either way. Wipe it on like it was stain, wipe the excess off, and let dry over night, and it is ready to go first thing in the morning. Shellac will stick to anything, so there are no compatibility issues.
One big issue here... GET RID OF THOSE OILY RAGS IMMEDIATELY. In the winter mine go straight in the wood stove. In the summer, they get spread out on the driveway to dry. DO NOT LEAVE THEM IN YOUR SHOP, they can spontaneously combust. I know a contractor in Missouri that burned their paint building down 3 times before they figured this out.
Spray the shellac thin, just like you would lacquer, but you have to be very careful if spraying it vertically. It runs and drools much easier than lacquer. So I lay my dulcimers flat on a turntable, and spray that way. It only takes a few seconds for the alcohol to gas off enough for me to turn the dulcimer over, or hang it up out of the way. I have a bed of nails on the turntable so the dulcimer is lying on the tips of the nails, not a flat surface. Standard paint room trick.
Best thing to do is 2 light coats, then let dry for an hour or so, then scuff down with 320# or 400# paper. Then another 2 light coats. The stuff will load your sandpaper so be prepared to use more than you would with lacquer. Shellac is by nature a high gloss finish. You can control the amount of gloss you get by how much you spray on. I want a satin gloss, or maybe just a little higher, so I stop at 4 coats. If you want more, scuff down again, and put on some more.
If the wood is sealed well, the shellac will build up a nice flat coat, and next day I can polish it. If it is rough, I will sand it flat with 400# paper, then rub out with 0000 steel wool, and carnuba wax. I use the Trewax brand from the hardware store. After buffing the wax, the finish has a soft matte glow, and feel that is out of this world. If the finish is fairly smooth, I will skip the steel wool, and only lightly go over the surface with a worn out piece of 400# paper to take off any dust motes that might be there. Then wax with a rag, no steel wool. This gives me the gloss that I really want, which is just enough so there is a little shine, but not glassy.
For the top of the dulcimer, since the bridges are not fastened down, I use Meguiar's #7 Glaze which is at the auto parts store. Wax is too slick, and the bridges might moved too easily. The Meguiar's seems to do the job just fine, and isn't so slick.
Color: Shellac comes in several colors depending on how refined it is. Platina is almost water white. Super blond has just a little color, you'd have to put on a lot to see it. Blond has some color, and is nice. Garnet is the old fashioned orange that you have seen on wood work in old homes everywhere. I use the dewaxed flakes. I like to mix Blond and Garnet shellacs. I mix up separate jugs of the two colors, and find a mix of 75% Blond, and 25% Garnet gives my birch ply a beautiful golden glow. I like this stuff a whole lot better than lacquer.
Top coat: If for some reason you want something else on the surface, you can use the shellac just for color coats, then top coat with anything. Shellac is the universal sealer, and anything will stick to it. I sometimes do this if I want the color, but also need the dependable semigloss of lacquer without the wax. Works fine.
So the disadvantages of shellac are that it is a little more complicated to do right, takes a little longer. I don't think it costs more, about the same as the Sherwin Williams lacquer I have been using. You also have to think ahead to have it ready when you need it. It also won't keep forever, needs to be used within 6 months of being mixed up.
But the advantages out weigh the disadvantages. I no longer need the HAZMAT suit. I do use the respirator, but as soon as the surface is dry, I can shut off the explosion proof fan in the spray room, and there is no smell at all! No gassing off for days, and making me sick. I can spray the shellac in the morning if I want to, polish it up after lunch, and we can put the strings on the same day. No waiting for several days for the dulcimer to quit stinking. Also no worries of sending it to somebody with a chemical sensitivity, and making them sick even after we can no longer smell it. And we are not supporting large chemical companies, instead we are supporting small business both in India, and here, like Shellac Shack. And it is much better for the environment.
