Repairing/Touching Up Polyurethane Varnish On Violins

[Thomas Knight]

VIOLIN AND INSTRUMENTS WITH POLY FINISH TOUCH UP--BY THOMAS KNIGHT

  Many student violins are covered with a thick oil based polyurethane varnish. This article may help luthiers repairing or touching up or these instruments.
  Polyurethane was invented in 1937 in Germany by Otto Bayer. Poly based coatings made their way to stringed musical instruments in the 70's and 80's. Thick and durable, these coatings have proven to be difficult to touch up, especially where a crack has been repaired. Traditional touch up methods prove incompatible due to alcohol (spirit) based varnishes being used. Oil based polyurethane does not feather well at the edges, and many times the fast drying spirit varnishes will pull up the edges making the repair even more noticeable. Water based urethane does not bond well to oil based poly. The obvious answer is touch up with oil based polyurethane, but staining this poly is difficult. This is because almost nothing dissolves or mixes into oil based polyurethane. 

  I researched and found that the chemical medium used by the industry to colorize poly is Glycol Ether which dissolves into oil based poly, alcohol, and/or water. It is the only substance I am aware of that does this. After some testing I had it down. Dissolve colorant into water or alcohol, depending on what the colorant is, mix the colored water or alcohol into glycol ether, strain off the residue of dye powder, and mix that with poly. It will be transparent and require 2-3 coats but will 'flow' into the repaired area and bond to the feathered/scraped poly perfectly and be impervious to chemicals, water, moisture, etc once cured. Working time is 10-15 min. Drying time is 6-12 hrs per coat.

  Some may object, but I use RIT powdered clothing dye instead of lake pigments. Yellow, dark brown, and dark red mixed to match are all I have ever used.

DIRECTIONS:
EQUAL PARTS DYE, WATER, GLYCOL ETHER (1:1:1)--THIS IS 'THE COLORANT'
THEN 1:1 COLORANT TO POLYURETHANE (OIL BASED MINWAX HIGH GLOSS)

STEPS WITH PICS:
I HAVE ADDED A PINCH OF SALT WHICH BRIGHTENS THE REDS IF NEEDED (PIC 1)
1:1 RATIO OF DYE TO WATER. MIX THOROUGHLY. (PIC 2) 

GLYCOL ETHER (PIC 3)
ADD 1 PART GLYCOL ETHER AND MIX. IT TAKES A WHILE FOR IT TO THOROUGHLY MIX.(PIC 4)
STRAIN OUT THE REMAINING POWDER RESIDUE (PIC 5)
USE EQUAL PARTS 1:1 DYE/WATER/GLYCOL MIXTURE TO POLYURETHANE (PIC 6)
ABUSED STUDENT VIOLIN WITH REDDISH POLY. EDGES CHIPPED OFF, WITH THINNER APPLICATION OF POLY THAN SOME OTHERS. (PIC 7)
ONE APPLICATION OF COLORIZED POLY (PIC 8)
TWO APPLICATIONS OF POLY (PIC 9)
 

[Mark Norfleet]

And just how did you determine that the student instruments are varnished with "oil based polyurethane varnish" ?!
I don't work on many "student quality" instruments any longer, but have in my time and believe you are mistaken.

 

[uncle duke]

Anybody can do an edge Mr.Knight but you may be on to something with other areas along the grain.

[Thomas Knight]

36 minutes ago, Mark Norfleet said:

And just how did you determine that the student instruments are varnished with "oil based polyurethane varnish" ?!
I don't work on many "student quality" instruments any longer, but have in my time and believe you are mistaken.

 

That is a great question. I should have addressed this. Oil based poly never fully dries unless it is catalyzed with a hardener, and even then it is somewhat softer than lacquer and spirit based shellac varnishes. If I have a question about the varnish composition I have a process which is fairly accurate. I also recognize the 'sheen' of newer poly finishes which look 'wet'. I must say experience is important, and I restored and painted exotic fiberglass cars, specifically Lotus, Avanti, Corvettes, and Panteras for decades and only a catalyzed poly based paint such as Imron or Amerflint should be used on a fiberglass car as the expansion rates from delta are very similar between polyester fiberglass and urethane paints. There is a certain 'look' to vehicles painted with lacquer, acrylics, or urethane paints. A trained eye can spot the difference a mile away.

  Most cheap Chinese are poly, and some mid grade as well. If uncertain I use q-tips soaked in a 50-50 Isopropyl alcohol-water under the fingerboard or next to the repair to see if any varnish comes off. If yes, it is spirit for sure. If no I try denatured, if yes, spirit and sometimes lacquer. and if no I go to acetone. Acetone will soften oil but be careful. Acetone will not dissolve poly. So if color comes off on acetone it is lacquer, spirit or oil. It can raise and curl feathered edges of poly, but not dissolve it. even I can tell a better violin and it is only the super-shiny student violins that have poly. Another way to tell if you are doing a repair that requires scraping or sanding of the crack's edge poly will not feather. You can see a defined line no matter how well you sand. Water based poly does this as well. You can touch up water based poly with oil based but not the other way.

[Violadamore]

Do you have any experience with urushiol/"cashew" lacquers or varnishes? 

[Thomas Knight]

4 hours ago, uncle duke said:

Anybody can do an edge Mr.Knight but you may be on to something with other areas along the grain.

 Yes, I was trying to show how it is thin, transparent, and has a flow characteristic that makes it a great option for crack repairs. I had a few people ask me about the coatings they were having issues repairing and they were poly varnishes. I know most of the luthiers here will be at an hourly price range where a cheap violin's repair would cost more than another violin of the same quality, but one shop owner I know has rentals and maintains them. I had dozens of student violins everyone here would know the names and they were all poly. When manufacturing switched to China every one I saw was poly. I hope someone out there who gets these in and repairs them can know for certain the mix I developed will work and is easy to make up. Glycol Ether is not hard to get but it must be ordered. Everything else is local big box or hardware store.

[Thomas Knight]

1 hour ago, Violadamore said:

Do you have any experience with urushiol/"cashew" lacquers or varnishes? 

I have had some Japanese (Nippon) violins with some unusual varnish on them. I assumed lacquer as acetone easily dissolved it and denatured takes it off, but slowly. I stripped many a violin in my early days before I was shown the error of my ways by the greats here on MN, so I had experimented back then a lot to see what worked.

[Thomas Knight]

My previous experiences always included stripping a vehicle or a golf club completely, then building it back up. In the mid 90's a music store in Miami went belly up and I bought a bunch of step up S&R former rentals from them and refinished them as they were in sad shape. Maybe refinished 100 student violins back in the day with poly and gave them to the local school systems. I used a spray gun and here are two I did. Found the pics. All were severely scratched, chipped, etc. The first was an S&R Germany and the second an early Eastman Scarampella. Both had been partially stripped so I stripped them how I was used to. These came out fairly good. I wet sanded with 1000 between clear coats. Binks #7 gun for those who know what that is. The S&R I buffed out afterwards which was a mistake. Poly does not buff out well. The Scarampella I wiped on a thinned out poly clear coat after wetsanding with 1000.

[Violadamore]

1 hour ago, Thomas Knight said:

I have had some Japanese (Nippon) violins with some unusual varnish on them. I assumed lacquer as acetone easily dissolved it and denatured takes it off, but slowly. I stripped many a violin in my early days before I was shown the error of my ways by the greats here on MN, so I had experimented back then a lot to see what worked.

Okay, that's a "no".  Cashew varnish, not polyurethane, is commonly used on Chinese violins, because they also use it on their traditional musical instruments, and over there, it's cheap.  The stuff is irreversible through oxidation cross-linking, and once cured, not affected by any solvent that I know of.  You need to research it. 

[FiddleDoug]

I once had an old MK instrument that someone had over varnished with PU varnish. It didn't stick well, and I literally had to peel this overcoat off the whole instrument.

[Thomas Knight]

1 hour ago, FiddleDoug said:

I once had an old MK instrument that someone had over varnished with PU varnish. It didn't stick well, and I literally had to peel this overcoat off the whole instrument.

Yes, that is usually from surface contamination or not letting a coat dry enough as once the outer coat cures the 'skin' prevents inner layers from outgassing. It will peel off just by rolling it up. *It is also why it wont feather well at all.

[Thomas Knight]

6 hours ago, Violadamore said:

Okay, that's a "no".  Cashew varnish, not polyurethane, is commonly used on Chinese violins, because they also use it on their traditional musical instruments, and over there, it's cheap.  The stuff is irreversible through oxidation cross-linking, and once cured, not affected by any solvent that I know of.  You need to research it. 

I will look into that. The only reason a poly repair would be used is the impossibility of feathering an edge on poly. I have a few fractional Suzuki parts violins. Let me see if a crack edge feathers. If it does then traditional spirit touch up varnish would be fine.

[Thomas Knight]

Here are three violin backs. The 'pink nightmare' is a cheap violin some poor soul bought for his daughter. Poly clear over pink paint. You can see when sanded the edge will not feather--the last attempt was 1000 grit. Impervious to denatured (right) and acetone (left) although the edge wrinkled and rolled a bit from acetone. Poly for sure.

The second violin is a S&R 2004 China. You can see it will not feather either, even with 1000. Denatured (right) nothing, acetone (left) wrinkled the edge. Also poly for sure.

Third violin is Suzuki 1978. Lacquer for sure--I know the smell. It is an unmistakable smell old show car bodymen and high end guitar luthiers recognize. Isopropyl no effect. Denatured (right) and acetone (left). Feathering the edge is very easy. Lacquer also produces a whitish 'powder' when scraping or sanding which is different than Shellac.

There are certain odors different finishes put out when sanded or scraped. Poly has a slight odor while shellac and lacquer are pungent.  Never could smell oil varnish.

 

[brokenbow]

Thanks--this is a useful technique for student violins, lots of other stringed instruments and furniture repair. Thanks for taking the time to prepare such a detailed explanation.  My ten minutes of Googling to find Glycol Ether turned up $80 US gallon jugs. Is there another source that you can point us to for Glycol Ether?

[David Burgess]

On 8/17/2021 at 10:38 AM, Thomas Knight said:

Here are three violin backs. The 'pink nightmare' is a cheap violin some poor soul bought for his daughter. Poly clear over pink paint. You can see when sanded the edge will not feather--the last attempt was 1000 grit. Impervious to denatured (right) and acetone (left) although the edge wrinkled and rolled a bit from acetone. Poly for sure.

The second violin is a S&R 2004 China. You can see it will not feather either, even with 1000. Denatured (right) nothing, acetone (left) wrinkled the edge. Also poly for sure.

Third violin is Suzuki 1978. Lacquer for sure--I know the smell. It is an unmistakable smell old show car bodymen and high end guitar luthiers recognize. Isopropyl no effect. Denatured (right) and acetone (left). Feathering the edge is very easy. Lacquer also produces a whitish 'powder' when scraping or sanding which is different than Shellac.

There are certain odors different finishes put out when sanded or scraped. Poly has a slight odor while shellac and lacquer are pungent.  Never could smell oil varnish.

 

Would you be willing to help me out by labeling each picture individually? I'm having trouble figuring out which pictures represent what..

A good violin restorer can feather just about anything, should that be desired. While I have learned a lot from my auto painting experiences, it's nothing even close to what a good fiddle restoration specialist can do.

I do appreciate your efforts to contribute, though.

[Thomas Knight]

2 hours ago, brokenbow said:

Thanks--this is a useful technique for student violins, lots of other stringed instruments and furniture repair. Thanks for taking the time to prepare such a detailed explanation.  My ten minutes of Googling to find Glycol Ether turned up $80 US gallon jugs. Is there another source that you can point us to for Glycol Ether?

Kolormatrix Industrial Coatings is what I use.

[Thomas Knight]

1 hour ago, David Burgess said:

Would you be willing to help me out by labeling each picture individually? I'm having trouble figuring out which pictures represent what..

A good violin restorer can feather just about anything, should that be desired. While I have learned a lot from my auto painting experiences, it's nothing even close to what a good fiddle restoration specialist can do.

I do appreciate your efforts to contribute, though.

 I will do that for you when I return this evening. Urethane in automotive use is mixed with a hardener and after a reasonable curing time can be feathered. Poly just wont. I would guess that oil based varnish would also work over poly for repair touch up as they dry slow. Never tried it. Alcohol based varnishes, like automotive paint, dry from outgassing the solvent used to mix or thin it. It is the rapid evaporation of the solvent that lifts the edges of poly. Polyester fiberglass also does not cure 100% and that is why Corvette and other fiberglass car restorers should use epoxy based two-part resin for restorations.

 

[David Burgess]

2 hours ago, Thomas Knight said:

 I will do that for you when I return this evening. Urethane in automotive use is mixed with a hardener and after a reasonable curing time can be feathered. Poly just wont.

 

Sure, polyurethane can't be feathered, if one lacks the skills to do it.

Pretty much like anything else.

Catalyzed urethane coatings were promoted as the be-all and end-all about 50 years ago, before people started to realize that they weren't.

A high-school friend of mine paid maga-bucks to have his car painted with that. It was guaranteed for life. The car had to be repainted twice in the next two years, but under warranty, at no cost to him. The car was totaled shortly after the second repaint job, and he's still alive ~50 years later, so we don't exactly know how all that worked out.

[Mark Norfleet]

3 hours ago, David Burgess said:

 

A good violin restorer can feather just about anything, should that be desired. While I have learned a lot from my auto painting experiences, it's nothing even close to what a good fiddle restoration specialist can do.

I do appreciate your efforts to contribute, though.

My thoughts and experiences exactly.

The only times I’ve found something difficult to feather is when a layer of colored coating was extremely thin and concentrated.

I have no doubt that the methods developed by Mr. Knight will be useful by many who repair such instruments.

[Thomas Knight]

  I decided the best way to settle this is to touch up a poly violin and post pics. This pink nightmare was bought for someone's daughter. I sanded it again with 320, 500, 1000 and micromesh 3000. Then I used spirit varnish, poly varnish, and brown oil varnish. I then put it in my UV box for 4 hrs. The poly and oil (IV # 1010rb) worked just fine. The spirit vanish is awful. This was only a single application with the poly and spirit thinned while the oil was right out of the bottle. The results speak for themselves.

  The violins I have encountered with poly finish that wont feather are entry level Stentor, Cecilio, Mendini, S&Roth after 2000 made in China, etc with a super shiny surface. Yes, some entry level like Eastman VL80 use lacquer. Some may use the cashew lacquer that Violadamore so accurately described. Those can be done conventionally. But the thick poly made in China rubbish (I love that word--thank you Jacob and Violadamore) is what I am referring to and you will not get the edge to feather. What I mean is you sand it or scrape and it looks feathered until a touch up varnish is added like most repairs that are spirit based. The edge will 'lift' as the solvent gets under the poly, then becomes a release agent, and will cause the poly to wrinkle like a cheap shirt collar after a wash. I shared my ideas here because a shop owner I met could not get the violin crack repairs to look right no matter what he tried. I can say without a doubt that a $100 pink poly nightmare violin sold on Ebay may never darken the door of the elite luthiers on this forum who repair and restore priceless instruments. There are, however, some of us who have encountered the poly and while it is only a few here or there I like to help solve problems.

Pic 1--top is oil, bottom right spirit, bottom left is poly.

Pic 2--close up of spirit reaction.

[David Burgess]

What are the ingredients in the spirit varnish, including the solvents?

Have you tried applying the spirit varnish in ultra-thin coats, with hardly any on the brush, rather than puddling it? Using a very dry brush will allow the solvent to evaporate more quickly, giving it less time to swell whatever is underneath.

Alternately, one might be able to apply a thin barrier/sealer coating of oil varnish, dry it, and then use conventional spirit retouching varnish on top of that.

[Thomas Knight]

It is a 1lb cut garnet shellac flakes with a very small amount of mastic gum thinned quite a bit with denatured alcohol--maybe to a 1/2lb cut. I believe an oil primer/sealer that is slow drying would work. The other reason for poly is the shine. Poly is available in high gloss so it will have the same sheen.

[David Burgess]

23 minutes ago, Thomas Knight said:

It is a 1lb cut garnet shellac flakes with a very small amount of mastic gum thinned quite a bit with denatured alcohol--maybe to a 1/2lb cut. I believe an oil primer/sealer that is slow drying would work. The other reason for poly is the shine. Poly is available in high gloss so it will have the same sheen.

So the solvent may be some mixture of methanol, ethanol, isopropyl alcohol, and who knows what else?

[Thomas Knight]

I mix up the flakes and gum but am not sure of the purity of the denatured alcohol I use. I also dont cook it but let it sit for a few weeks.  I get DA at the big box stores and don't bother to distill it to remove the water. I have used grain alcohol which seems to flow better while brushing and dries a little slower but the cost difference is notable and I never feel comfortable going into a liquor store. Sounds ridiculous but I dont drink alcohol and never go in one.

[David Burgess]

4 hours ago, Thomas Knight said:

I mix up the flakes and gum but am not sure of the purity of the denatured alcohol I use. I also dont cook it but let it sit for a few weeks.  I get DA at the big box stores and don't bother to distill it to remove the water. I have used grain alcohol which seems to flow better while brushing and dries a little slower but the cost difference is notable and I never feel comfortable going into a liquor store. Sounds ridiculous but I dont drink alcohol and never go in one.

Going into a liquor store to buy 95+% alcohol is nothing that one need be ashamed of. They know what's up. The last time I bought some (three bottles), the counter person said, "Oh, you must be a woodworker".

When I went back out to the parking lot, I got involved in a conversation with a really drunk guy. He had just purchased another 24-pack of beer. Really friendly guy. Hope he made it home OK.