Sun tanning your instrument

[D. Piolle]

My guess is that that's not photo-degradation, but oxidation.  If it was photo-related, I don't think the grain direction would matter, and it would darken evenly.  For oxidation, where the grain is parallel to the surface, it won't oxidize as deeply compared to where the grain runs more steeply at the surface.  I think the deeper oxidation/darkening depending on grain direction would cause the partial fixing of the flame.

 

For the old violins that started life with varnish, you don't get the oxidation for a long time until the varnish wears off.  Even then "worn off" might not be completely so, as perhaps there's still something plugging up the grain to prevent oxidation... sweat, dirt, French polish...

Could that be both photo-related and oxidation. Oxidation is surely faster with some heat by the way. But I noticed even in hot weather, with undirect daylight, the color is not the same as wood exposed to direct sunlight and it takes much longer to get a color that can be relevant and significant. One of my soundboards left aside for several years darkened with time ( natural oxidation with no exposure to sun ) , it has a nice color but doesn't compare to any piece of wood exposed to the sun, (I will post the picture as soon as I can). Though I ' m not arguing which one is better.

I already posted pictures in another thread by Davide Sora.

Here are some of them: the 1st one is a piece of maple exposed to direct sunlight, the lightest part was actually hidden by an aluminium foil during the whole exposure... the 2 last ones are the result on one of my violins ( with some ground and first layer of clear varnish).

[Michael_Molnar]

I don't doubt that oxidation is enhanced by light. 

 

As to John Harte's point about blue light effects, I suspected that something like this was happening. That is ordinary light could penetrate deeper into the wood than UV. Thus it seems that there is more than one photo-reaction at play. I wonder about infrared (heat) effects that could accelerate surface reactions with moisture. Fascinating stuff for sure.

[joerobson]

In what range of temperature / humidity / sun conditions are you comfortable with putting your white instrument outside to darken?

For how long do you keep it out there at a time?

Do you turn it often?

Any other suntanning cautions and tips?[/quote)

So Michelle... To answer your question: I don't tan.

Joe

[Jeffrey Holmes]

 

The color of the wood is far darker than we see in the exposed areas of Cremonese instruments.

 

I can think of some Ruggeris in which the wood is quite dark under the varnish... especially the tops... and the color goes deep into the wood. I always wondered if it had something to do with how/where the wood was stored before use.

[Christopher Jacoby]

Store it in the rafters over the tanner's vats...

[pbelin]

Don, I have tried several things with processed wood..

Several weeks in a uv cabinet show a strong yellowing on light processed wood (not as dark as your stuff)

Bleaching... I have had no success, either with chlorine, h2o2, oxalic or citric acid.

If old wood is dark and opaque all the way through, I see no reason why the outer surface should be any less dark, or do you think the contact with the ground would prevent the wood from darkening?

[Don Noon]

Bleaching... I have had no success, either with chlorine, h2o2, oxalic or citric acid.

If old wood is dark and opaque all the way through, I see no reason why the outer surface should be any less dark, or do you think the contact with the ground would prevent the wood from darkening?

 

You should review the wood bleaching thread http://www.maestronet.com/forum/index.php?/topic/333448-wood-bleach-to-lighten-dark-wood/

High-strength H202 is not going to do much without the hydroxide treatment first.

 

Assuming natural darkening is a result of some combination of oxidation and UV exposure, then any coating that keeps out oxygen and/or UV should severely cut down on those changes.  

[pbelin]

Thanks, I missed this thread!

[~ Ben Conover]

Not sure if I mentioned it before but shrinkage of spruce should be factored
when tanning for months at a time. A free viola top can shrink 3mm in width,
how do I know that...

 

[David Burgess]

Not sure if I mentioned it before but shrinkage of spruce should be factored

when tanning for months at a time. A free viola top can shrink 3mm in width,

how do I know that...

 

What was the relative humidity inside the tanning enclosure?

[Don Noon]

Not just relative humidity, but the surface temperature of the plate vs the air temperature too.  You can get a decent RH reading, but if the wood is much hotter than the air, it's going to dry out more than you might expect.  Strong lights and moderate air flow will do it.  Or leave wood in the sun...

[joerobson]

If you are keeping the instrument in the tanning box for an extended period of time you should cycle it out of the box on a regular basis.

[~ Ben Conover]

'' What was the relative humidity inside the tanning enclosure? ''
It's not an 'enclosure', just a small room with the window and door left open.

It's very humid in Ireland, and the plate had been sitting on a shelf prior to tanning
for some months, so (as you imply) the difference in humidity was probably massive.


 

[Don Noon]

Old fidels that have not been worn down to bare wood will not have acquired a sun tan.  

Just as a new violin (Joe will disagree here but hopefully he's asleep) won't get a tan

through the varnish, and so remain quite pale under the varnish for a very long time. 

 

 

I have no clue what the SPF of varnish is, or how it compares to the lacquer that was used on my Collings guitar... but for sure it got noticeably tanned when I intentionally put it in the sun for a couple of days after I got tired of looking at its pasty-white newness.

 

I just put out a maple sample in the sun with some clear varnish on part of it to see what happens.  The sun's not terribly strong right now, though.

 

We had a few (most of them) sunny days recently, so here's some maple with about 3 or 4 days total sun exposure.  It was still "winter" sun, but stronger than most other places.  The photo is the same sample, just two different angles.

 

The wood is over 30 years old, but just recently cut from a cello billet.  Very little seems to happen deep inside the wood, from what I can tell.

The zones are as follows:

1 - bare wood, sun

2 - bare wood, no sun (covered with aluminum foil

3 - ground + varnish, no sun

4 - ground + varnish, sun

5 - ground, no sun

6 - ground, sun

7 - bare wood, sun

8 - bare wood with SPF 50 sunblock

 

Fairly apparent from the photos is that bare wood and light ground both darken appreciably in sun, and that varnished wood is less apparent.  Still, looking at the sample from different angles, the shaded area of varnished wood appears slightly lighter.

 

It is my impression that the suntanning of the bare wood puts a uniform tan color everywhere, and therefore reduces the contrast and chatoyance.  I suspect this is because the tanning effects are limited to the extreme outer surface, like adding a colored film over everything.

[Michael_Molnar]

It is my impression that the suntanning of the bare wood puts a uniform tan color everywhere, and therefore reduces the contrast and chatoyance.  I suspect this is because the tanning effects are limited to the extreme outer surface, like adding a colored film over everything.

That is my conclusion too.

[Janito]

It is my impression that the suntanning of the bare wood puts a uniform tan color everywhere, and therefore reduces the contrast and chatoyance.  I suspect this is because the tanning effects are limited to the extreme outer surface, like adding a colored film over everything.

 

Isn't that the same as the 'Noon' processing and likely to be the effect of long aging seen in old violins (the wood inside can be pretty dark)?

[Don Noon]

Isn't that the same as the 'Noon' processing and likely to be the effect of long aging seen in old violins (the wood inside can be pretty dark)?

 

Nope, not the same at all.  

 

Tanning only darkens the outer surface.  Processing darkens the wood uniformly throughout.  Aging of a varnished instrument... I'm not sure, as there is undoubtedly some preservation of the surface by the varnish, some UV might get through the varnish to darken the upper part of the wood, and then oxidation progressing from the interior.  Sun tanned wood is not opaque; processed wood and old violins are.

 

I think that a darkened surface with the rest of the thickness being white/translucent (as you would get with tanning) will not give the same appearance as wood that is uniformly opaque, as you get with old violins or processed wood.  That is not to say that processed wood and old violins look the same... there's still the overall color that can be different, and the old violins may have a surface color different from the lower layers, whereas processed wood is uniform.  

 

Sound isn't the only thing that's ridiculously complicated.

[pbelin]

About processing, (sorry that's a bit off subject) what would be the difference between vacuum chamber and pressure cooker (with steam)?

[Don Noon]

You need the water vapor to for hydrolysis of the hemicellulose, which is like reducing the resin content in a carbon fiber material.  You get better stiffness/weight up to the point where the fibers fail to hold together.

[pbelin]

Thank you!