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Polyurethane

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I recently tested polyurethane (Minwax Wipe On Poly in gloss) by applying 3 generous coats to a sheet of Saran Wrap. After the third coat had dried thoroughly I wrapped the Saran around a soda straw. There was no flaking or cracking and the finish seemed to hold up quite nicely.

Its a bit "outside the box" but does anyone have experience using it on a violin? Seems like a no brainer but I've never heard of it being used as such. What am I not considering about it?

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Don't even think about it.

1) It is likely to damp the sound.

2) It's very fussy about what it sticks to. I once had to literally peel a layer of PU off of a violin (I didn't put it on).

3) It's impossible to touch up or repair after it has cured. The can probably says to sand the surface.

4) You might not be able to tint it properly.

There are other commercial varnishes out there that people, including myself, have used successfully. These are generally like oil based spar varnish. Ace Hardware used to have it in quart cans, but now only gallons.

Something like this product may work,

http://www.rustoleum.com/product-catalog/consumer-brands/zinsser/interior-wood-finishes/bulls-eye-spar-varnish

In any case, avoid things like urethanes, and test any varnish system (including the ground,sealer, and tints) on scrap wood,before you even think about putting it on an instrument,

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You could try Tru oil, which I think is a type of linseed/alkyd varnish. It's a thin wipe on finish but it can be brushed on (very easy to brush). It dries relatively fast, probably because of the added driers. On a test piece I brushed on 8 or 9 coats in one long day (one single UV light in the cabinet) and rubbed it all out to flat gloss the very next day! I mean guitar flat gloss too. The woodwork was taken to a very high grit which obviously helped to achieve a finish in such a short time. Of course there's no need to rush. I was just finding out if it could be done.

No colour though (or very little).

It's also readily available.

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To the OP, I think the issues are potential impact to sound would have to be tested to determine if it is acceptable to you. But most important issue is repairability as FiddleDoug mentioned. If you are making/restoring a disposable violin, meaning something you will use and then throw away later, it might be okay, if you want something that will last generations, it is probably not the best choice. And don't get me wrong - disposable violins probably have a place (market?) I just am not aware of it. And of course what is you own goal for making/refinishing the violin is important.

 

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1 minute ago, Brad Dorsey said:

How does the Saran Wrap sound?

With my hearing aids on, it is definitely very bright and tinklely - once varnished, it might sound better :)

 

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49 minutes ago, Michael.N. said:

You could try Tru oil, which I think is a type of linseed/alkyd varnish. It's a thin wipe on finish but it can be brushed on (very easy to brush). It dries relatively fast, probably because of the added driers. On a test piece I brushed on 8 or 9 coats in one long day (one single UV light in the cabinet) and rubbed it all out to flat gloss the very next day! I mean guitar flat gloss too. The woodwork was taken to a very high grit which obviously helped to achieve a finish in such a short time. Of course there's no need to rush. I was just finding out if it could be done.

No colour though (or very little).

It's also readily available.

and very inexpensive.

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Polyurethane need not be any more difficult to apply and repair than a traditional oil/natural resin varnish. It is just as easy to screw up the application of either type of varnish if you do not spend the time to understand how they adhere, cure and accept additional coats.

Typical commercial polyurethane varnishes seem to have a higher sound damping ratio than oil/resin varnishes, but the affect on the violin's final sound can be difficult to assess since it depends on how much of the varnish is applied, and how deep it is allowed to penetrate into the wood.

Modern polyurethane varnishes have extremely high transparency across the entire visible spectrum, and very little reflectance. The transparency is very stable over time, as is the integrity of the film. It is resistant to just about any liquid you can throw at it and is ideal for surfaces that will be handled repeatedly.

Oil/natural resin varnishes are more susceptible to transparency and integrity changes over time, especially if the proportion of oil is high relative to the resin. They do not wear as well as polyurethane, and are more susceptible to damage from common liquids.

So why oil/resin over PU? Well, refractive index for one. Oil/resin varnishes have refractive indexes that are typical of the wood, so can optically enhance the grain and figuring of the wood. PUs have lower refractive indexes that give what is sometimes called a "plastic" sheen to the wood. In other words, the best oil/resin varnishes appear to be an extension of the wood surface, while a PU varnish can look more like a cover sitting on top of the wood.

I am not sure tint is still a reason to prefer oil/resin over PU. With the advent of water-based urethane varnishes and a large selection of stable water-based dyes, one can make a transparent polyurethane varnish of any color one can imagine.

Edited by ctanzio
color-based to water-based

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On 8/2/2017 at 6:56 AM, FiddleDoug said:

Don't even think about it.

1) It is likely to damp the sound.

2) It's very fussy about what it sticks to. I once had to literally peel a layer of PU off of a violin (I didn't put it on).

3) It's impossible to touch up or repair after it has cured. The can probably says to sand the surface.

4) You might not be able to tint it properly.

There are other commercial varnishes out there that people, including myself, have used successfully. These are generally like oil based spar varnish. Ace Hardware used to have it in quart cans, but now only gallons.

Something like this product may work,

http://www.rustoleum.com/product-catalog/consumer-brands/zinsser/interior-wood-finishes/bulls-eye-spar-varnish

In any case, avoid things like urethanes, and test any varnish system (including the ground,sealer, and tints) on scrap wood,before you even think about putting it on an instrument,

Thank you, FiddleDoug. I never considered the repair angle. I might pick up some of the zinsser product and experiment with it.

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