Speeding up suntanning


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16 hours ago, Per Ovesen said:

Any suggestions on how to speed up the “suntanning” process in a uv light box? Lower or higher humidity etc?

Orbit it around the earth to get full blast unfiltered sunlight! (Just kidding)

If you are talking about how to get quicker a yellow tint, it seems that washing the wood with soap works pretty well. I heard it from the wood dealer Fuchs in Mittenwald. He sold always this nice yellow maple and when I asked him how he made it he shrugged his shoulders saying: Nothing special, I wash it with soap and then put it on the grass in the sunlight for one day. In this context I should mention that the oxygen produced by the grass in the sun seems to play a role as well. (In ancient times cloths were bleached with this method)

Instead of soap you can use  baking soda (which seems the active ingredient in soap) as well and then sun tanned them. Works better on spruce than on maple. If you don't like the soda in the wood you can wash it out with water after sun tanning.

On a technical level a stronger lamp helps but can be risky because the humidity drops in the tanning chamber.  (I once cracked a top with it, thereafter I kicked the lamp out of my workshop.) I would say better put more UV tubes is a better solution.

Good to see you here, Per!

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Hi Per.

I can't help thinking that some moisture in the wood helps, a bit like metal rusting, so I take the violin out, mist it with water, and leave it overnight occasionally. I also have a pot of water in the bottom  of the light box, although I'm not sure that it does much.

I'm pretty sure that fresher wood tans more quickly than old wood, and it develops the ripple in the flame too. If I could, I'd make my violins with fresher wood, and just hang them to season for a year in a bright place.

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7 hours ago, FiddleDoug said:

" Instead of soap you can use  baking soda (which seems the active ingredient in soap) "

Actually, baking soda has little to nothing to do with soap.

Brighter/more lights are the only real way to go. Keep the heat down with a fan.

Hard soap is made with fat and sodium hydroxide or soda carbonate (= baking soda).

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Potassium hydroxide. Lye. Alkaline ..a strong corrosive is used with fats acidic to make soap. Wouldn’t,t use either as they are alone but combined are good for cleaning.      because water will absorb free Oxygen as it evaporates would leave that Free stuff behind in the wood available.maybe enriching the water with a bubbler would increase it,s effectiveness, as might using a deionized water , one with more room for the oxygen as it does not containing minerals. The nitrates are oxidizer as well , but they produce in their decomposition nitric acid, so must be used sparingly at low concentration so as to not cause long term damage. 

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Keep in mind that there are many different compounds in wood so there is potentially many different types of chemical reactions that can occur that result is color change.

I tend to think of wood compounds in two general categories: permanent and extractive.

Permanent compounds are things that give the wood its basic structural integrity, like lignin, cellulose and hemicellulose. Casual, short term application of solvents, like alcohol and water, has little affect on these.

Extractive compounds are things that are easily removed or added by application of solvents or physical processes like heat and humidity. Resins, oils and water are all examples of extractive compounds found naturally in wood.

As a general rule, coloring processes that target permanent compounds tend to cause permanent and uniform coloring, while those targeting extractive compounds tend to cause temporary or inconsistent coloring.

UV treatment tends to work strongly on the lignin, a permanent compound. UV + Air = lignin breaks down and eventually forms a stable, yellow compound that is non-extractive. But lignin is also the "glue" that holds the cellulose and hemicellulose structures together. So excessive UV exposure risks compromising the structural integrity of the wood.

UV can also cause chemical reactions in the extractive compounds of wood. My current thinking is that "seasoning" the wood, mostly by exposure to reasonable heat for a period of time, causes a good amount of the extractives to evaporate out of the wood. It is difficult to say if this is always a desirable or undesirable thing, but it at least reduces the effect of some variables from the UV tanning process.

The rate and intensity of UV tanning is proportional to the intensity of the UV (more lamps and/or higher wattage) and the amount of unoxidized lignin exposed to the UV light. So the tanning process starts out rapidly but quickly tapers off as less un-oxidized lignin is available to the light.

To reduce the tanning time, you need to use higher wattage bulbs or more lamps. Make sure the wood remains well ventilated so there is adequate oxygen to complete the chemical process, and do not allow the wood to become overly hot as this risks driving other chemical reactions which can cause unexpected results.

 

 

Edited by ctanzio
grammar check
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Unless this is the only instrument you're going to make, tanning isn't really down time.  It happens in the background while you're working on other stuff.  I guess I don't really see a need to speed things up.  There could be a question on how long should it take?  If there is something wrong with your equipment or the set-up that's another situation.  For me, the wood looks about right in the ball park of 240 hours with my lights and set up.  If all of sudden that time jumps to 400 hrs. (for example), then maybe it's time for new bulbs.

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The one time I put baking soda solution on wood it turned and ugly greenish gray.   Other alkalis seem to have the same result.   And what kind of soap would you use?   Then after tanning you would have to rinse it off?   wash rinse repeat?

 

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1 hour ago, Michael_Molnar said:

Sometimes I wonder whether "full spectrum" sunlight is superior to a UV cabinet. Of course, UV has the energy to effect changes, but the IR might help in another manner. Just thinking out loud. 

I think it is. At least, things seem to tan faster outside than in the lightbox.

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1 hour ago, Michael_Molnar said:

Sometimes I wonder whether "full spectrum" sunlight is superior to a UV cabinet. Of course, UV has the energy to effect changes, but the IR might help in another manner. Just thinking out loud. 

Let’s see. This morning before work I planed and rounded the end grain of some belly and back cut-offs down to fresh wood for the viola I’m making for test varnishing. I put the two pieces in my light box to tan. Basically trying to do things as near to how I will varnish the instrument. 

Just now I planed another cut off of the same belly and back that I will exclusively tan with the sun.   We’ll compare in 10 - 14 days. The sun tanning will be unpredictable because of rain days and the annoying habit of the earths rotation. 

  1BAAAB56-70AD-4B2B-8F20-7AE315C00B2B.thumb.jpeg.9faa0fbe68ba0cc52531b04d317c27e6.jpeg

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7 hours ago, Michael_Molnar said:

 but the IR might help in another manner. Just thinking out loud. 

Interesting you say this. I was thinking the same thing scrolling through the previous posts before reading your post. Strong IR will indeed darken and yellow the wood, before it's starts turning brown and beginning to char. At moderate levels, it may be controllable and advantageous.

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One thing to consider is moisture reduction when tanning. A violin looses 15-20 g of weight during the process. This makes a lot of stress to the plates (especially the backplate) as moisture is drawn out from the outside surface. As a precaution, if you have a soundpost installed take it out before starting

The opposite happens when you stop tanning. I like to wait for a couple of days before I start the varnishing process. 

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