UV Lights for Curing Varnish

[Steve Hinde]

What is the correct light to use for curing varnish? I have scanned the archive and didn't find a clear answer. I understand the dangers and will take ample precautions to control the access to the box and light controls.

I will add a ventilation fan to control the heat and just pull in room air to keep the humidity up. Vent it out side of course.

[sunburst]

Does the varnish manufacturer have a recommendation?

[HoGo]

Steve,
need for artificial UV depends on type of oil varnish you use (spirit or other evaporative varnishes don't need light). The commercial spar varnishes don't need any extra UV though it will speed up drying a bit. Traditional violin varnishes with unprocessed oil in them would take days to dry after each layer and need direct sun or other source of UV.
I use both types and use small Phillips suntanning unit I bought at pawnshop, it has four UVA tubes (5Watt each?) and works well. You can buy spare tubes and make your own box lined with Al foil and with some ventilation holes in both bottom and top, some folks add PC cooler to draw air in or out. these tubes don't produce much heat at all so all this may not be necessary. Don't over humidify (slows drying and may cause adhesion problems) small pot with water in the box is usually enough to keep the humidity in 40-50% range.
You should check violin forums for more info and pics. Try maestronet forum.
Good luck.

[Big Joe]

Look for UV lights in the B and C spectrum for best results.

[Steve Hinde]

Thanks Joe. That is what I was looking for. John, I will ask my supplier. I should have thought if that.
Adrian, thanks for the advice. If I need an answer, I just post a question here.

Steve

[Geoff B]

Piggybacking off that, I'd be interested to know if Behlen's Rockhard Table Top varnish cures faster with UV light, and if so, which form (A, B, C, etc.)? I like it, but I'd like it more if I could shorten the time between coats.... couldn't find info at the Behlen's site....

[HoGo]

UV B or C will speed up the drying more than UVA but it's much more dangerous to your eyes. This has been discussed over in the violin forums and folks who use UVA report just as fine results as the others. Good UVA tube will dry traditional oil varnish overnight so there is no need for anything stronger unless you want to recoat twice a day.
I'd say the UV would speed up the Behlens RH but it will dry overnight without it so why bother... Perhaps if you want to counteract high relative humidity or use of solvents (some solvents will slow down polymerization of oil). Make sure the coat is dry before applying next layer or drying of next layers will create crazing.
Also difference in UV A-B-C is not only in their "intensity" but also the UVA penetrates deeper than B and C. I don't know if this makes difference with film of such thinness.
One side note. Gibson during "Loar Era" didn't have any UV lights and it worked just fine for them. :D

[Big Joe]

Well, there were UV lights, but it was usually natural . Sunlight is still a great source of UV, though not very programmable.

[Mario Proulx]

Sunlight is still a great source of UV, though not very programmable.

As far as its varnish curing abilities, the sun is pretty consistent. Clouds don't protect us from UV rays, and in fact, we're more likely to sunburn on cloudy days. So... a small, air conditioned(as simple as a thermostat triggered fan may do for most of the year) "greenhouse" might be the best deal for a varnish curing cabinet.

I've "cured" many a project in the driveway...

[Michael Lewis]

Adrian is right, Behlen's RH dries quickly compared to most other finishes. There is no need or useful application of UV with that finish. That is one reason I favor it, that, and the fact it gets pretty hard.

[Steve Hinde]

I have not tried the Behlens Rock Hard. I am running a test on several different materials right now and will throw that in the mix. If I don't have to cure that is a great idea. I don't build fast enough to need 1 day turns, but I don't want to wait 4 or 5 weeks either. Again, you advice is invaluable.
Thanks!

Steve

[sunburst]

For sure give Behlens RH a try.
About the only thing I don't like about it is the dark amber color, and I can live with that. Get the smallest quantity you can, and don't leave a can half full or it will cure in the can.

[Steve Hinde]

So, what do you guys suggest as the best 'clear' varnish? The amber color is a problem on some colors. I like the earthtones and natural colors, but I have done some Burgundy and Blue that the amber would definitely mess with. In the past I used lacquer on other instruments and a couple mandolins, but I prefer the varnish on the mandolins for tone. I made 1 white violin a couple years ago using violin varnish from International Violins and I got away with it. But I added Titanium pigment to the varnish. It took about 8 weeks to cure out enough to flatten and FP out. That is why I am asking about the curing. I've been working on other instruments for a while and getting back to the mandolins, I want to focus on the finishing and settle on some preferences. Lacquer is an option, but in the winter I can't spray, so I need other options. I am testing a couple of spar varnishes that are pretty clear, but durability, curing, etc are a concern. I've had to refinish a couple instruments, and that is not my idea of fun.

[sunburst]

Behlen sells "Water White Restoration Varnish". The main difference between it and Rock Hard is the amount of oil; RH is a short or medium oil varnish and WW is a long oil varnish. That means the WW cures softer, but it is pretty darned clear. I've tried it on scrap and it dried fine and not noticeably soft, and I've also mixed it with RH to get an intermediate hardness and less of the dark amber color. That worked fine too.

By the way, the reason for the soft, long oil formula for the restoration varnish is that restoration often involves applying new finish over old. As long as the varnish is softer than the old finish that is under it, it isn't likely to craze and check. Also, the clear color helps maintain the look of restored furniture when new finish is applied. There are also some spar varnishes that are nearly colorless. Spar varnishes are softer that RH because they are meant for outdoor use with the wild temperature swings associated with that, they are also normally full of UV blockers that aren't really needed on instruments, but quite a few folks have used Z-spar and Epiphanes varnishes on mandolins. Most modern spar varnishes have polyurethane or alkyd resins as opposed to the phenolic resin used in the Behlens varnishes mentioned above.

[Steve Hinde]

Thanks John. I'll do some trials with that too. I like to get a feel for the material before I actually put it on an instrument. I did learn that lesson.

Steve

[woodwiz]

Behlen sells "Water White Restoration Varnish". The main difference between it and Rock Hard is the amount of oil; RH is a short or medium oil varnish and WW is a long oil varnish. That means the WW cures softer, but it is pretty darned clear. I've tried it on scrap and it dried fine and not noticeably soft, and I've also mixed it with RH to get an intermediate hardness and less of the dark amber color. That worked fine too.

By the way, the reason for the soft, long oil formula for the restoration varnish is that restoration often involves applying new finish over old. As long as the varnish is softer than the old finish that is under it, it isn't likely to craze and check. Also, the clear color helps maintain the look of restored furniture when new finish is applied. There are also some spar varnishes that are nearly colorless. Spar varnishes are softer that RH because they are meant for outdoor use with the wild temperature swings associated with that, they are also normally full of UV blockers that aren't really needed on instruments, but quite a few folks have used Z-spar and Epiphanes varnishes on mandolins. Most modern spar varnishes have polyurethane or alkyd resins as opposed to the phenolic resin used in the Behlens varnishes mentioned above.

I'm making an educated guess based on experience, but the resins in Behlen's Water White Restoration varnish are probably soy alkyds, since they are the lightest colored varnish resins in common use. They are not as hard as the Phenolic resins in Rock Hard.

Pratt $ Lambert's "38" varnish is a very light colored soy alkyd as well. Good stuff, but I don't know how well it polishes.

There are actually vinyl varnish resins on the market now. I have no experience with them.

[sunburst]

I'll check the label again and report back later, but I remember Water White being phenolic.

[Mario Proulx]

The Pratt & Lambert "H38C" polishes and buffs beautifully. Tough, also. I've only used it on one mandolin, but I have used it a good bit on other woodworking projects. It's my go-to varnish, when I can find it(spotty supply up here). And yes, it gets the "driveway UV cure" treatment also

[sunburst]

For what it's worth, the Water White label does say it is a phenolic resin varnish.