A UV Varnish Drying “Cabinet”

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Drying Varnish

There is a saying in violin making that it takes about only a few years to learn the basics of constructing instruments, but it takes the rest of your life you learn varnishing.  A UV Varnish Drying cabinet can speed up the entire finishing process.

Traditional oil varnishes are a combination of drying oil (for example, walnut or linseed), a resin (for example, copal or amber), and a thinner.  While initial drying of varnish is accomplished by the evaporation of the thinner, the curing of the varnish is a chemical process; the varnish alters at an molecular level.   The curing, or polymerization, of the varnish is accelerated by UV light.  Alcohol based varnishes, notably used in the French tradition after the Cremona golden period, do not require this method.  Based on my research, I’m certain that the Cremonese makers used oil varnish.

Tanning instruments (both in the white and after coats of varnish) is a common technique in violin making.  Exposure to artificial UV light effectively replaces exposure to sunlight.  This is useful in areas which have lower sunlight exposure due to winter, or where exposure to direct sunlight isn’t practical (the glass in household windows blocks a large portion of UV light).  Aside from curing varnish, sunlight is also used to ‘tan’ an instrument which darkens the flaming of maple.

CAUTION: exposure to UV light causes cataracts and skin cancer, just like over exposure to the sun.  The bulbs I recommend below should be fairly safe for short period of exposure, but its best to avoid prolonged exposure.

The UV cabinet is a tool which provides a way to accelerate the exposure of the instrument to UV both for tanning of the bare wood, and accelerating the curing of the varnish between coats.  An instrument may be tanned for one or multiple weeks, while varnish exposed to UV will cure overnight.

 

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The UV “Cabinet”

A simple, cost effective method of building a UV cabinet is the steel can cabinet.  Not glamorous :), but certainly low cost and functional.  This consists of a galvanized steel rubbish bin or garbage can, with UV florescent lights mounted vertically inside the can.  A small amount of electrical expertise is required.

 

A 91 liter (24 US Gal) can is used and is sufficient for violin building purposes.   Lights for terrariums can be sourced from pet stores (I used Exo-Terra “Repti Glo 10”, T8 style 24” 20W bulbs).  The bulbs require a fixture (T8 24”) which can be found at a home improvement store, make sure it comes with a ballist.  A disused extension cord wires it all together.   The rubbish bin is about $30, the T8 fixtures are about $20 each, and the T8 terrarium bulbs are about $30 each.  In my UV enclosure I have 4 bulbs, but three might suffice.

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Terrarium Bulbs Provide Sufficient UV

Overall this is a simple electrical project.  The fixtures are wired in parallel to the mains, but if you’re not sure what that means, get a friend who knows about household wiring to help you out.  It’s a good idea to wire the steel can to earth ground, this will prevent any shocks from accidental shorts and will safely trip your household breaker.

 

These florescent tube bulbs are more energy efficient than a typical incandescent and better for the environment than a compact fluorescent.   They do produce some heat however, and if the lid of can is fully closed the air inside will rise to the mid 40’s C (110F).  This will dry an instrument and may stress it.  Hence it’s better to leave the lid open by several centimeters (an inch or so) to allow air to circulate.  If you do this, put the can in an unused location to avoid exposing people or pets to excessive UV.   As well, receptacle mounted timer units can be found to switch the lights on and off periodically.

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A dowel prepared dowel is useful for suspending the instrument

The unfinished violin can be suspended inside by the button hole or under the scroll at the top of the peg box.  The naturally reflective galvanized coating acts to efficiently reflect the light inside the box.  The steel container is naturally heat and fire resistant .

 

Like all fluorescent bulbs, the power of the bulbs diminishes over time before finally burning out, so replacing them periodically will produce better results.

Some alternatives exist.  For larger instruments entire cabinets are setup.  Also, today, the terrarium bulbs are available in compact fluorescent.  Black lights are sometimes used in place of terrarium bulbs, however, but I suspect their UV output is considerable lower.  Others have used tanning bed bulbs, but they typically come longer than the 24″ used here.

Guy Harrison engaged a local lighting shop in Ottawa to come up with a strong UV light.  This light was a modified 250W mercury bulb.  I spoke with the lighting shop.  A setup for mercury lights costs a fair bit more than for fluorescents.  As well they modified the bulb by removing the borosilicate outer shell.  These bulbs produce a large amount of UVC which is particularly harmful.  Anyone experimenting with this method should be very caution about over exposure, but Guy’s results were quite impressive.

2 responses

  1. Excellent article and very useful as I’m studying up on how to reasonably manage uv varnish drying. Do you know whether the unit can be used in the usual workspace or if it is necessary to place it outdoors to avoid exposure to ozone, etc.?

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