Monday, September 28, 2026

Does UV-C light speed polymerization of Boiled Linseed Oil? maybe a little)

 One camp says UV (such as in sunlight or from mercury vapor lamps - the shortwave stuff, not blacklights - hastens the curing of BLO, the other camp says no, only oxygen matters, and not even heat will speed up the process because it is not drying in the usual sense. Evidence - and I'm here to tell you that most woodworkers are not good scientists - suggests it's a little of each column.

 We are Fooling Around with every intention of Finding Out:

100 watts (electrical) of short-wave UV

 I actually put cardboard around it because I wanted to work near it, and use the bench, and even the stray scattered light from these things will give you - and your corneas - a sunburn, with bonus increased risk of skin cancer thirty years later.  Stay away from the evil-looking death light. :D

The strongest peaks in the mercury vapor spectra are:



Wavelength (nm) 
Name 
Color
184.45
ultraviolet (UVC) - !!
253.7
ultraviolet (UVC) - !!
365.0I-lineultraviolet (UVA)
404.7H-lineviolet
435.8G-lineblue
546.1
green
578

yellow




 

 The brightest peaks are the UV, blue, and green lines, which is why it looks like an eery sort of blue-green color to our eyes.  The yellow line is weak, and I suspect we can all be grateful for that.  They used these in street lights (for you youngsters) before LEDs and before those, High Pressure Sodium.



 UV light speeds polymerization of some resins, and with the UV-cure resins used in 3D printing for example, it can just be UV-A (blacklight, harmless).  But in theory, higher-energy photons should do a better job of polymerizing, right?  Well, we get higher-energy photons by going to a shorter wavelength.

 Kids don't try this at home; shorter wavelengths (UV-B & UV-C) will not only sunburn your skin, they will sunburn your corneas.  (feels like sand in your eyes for weeks, and can cause permanent damage to your eyeballs.  You need goggles or UV-coated eyeglasses at the very least.  Thick glass lenses alone will stop UV-C, but for UV-B you need an anti-UV coating.

 EDIT: early indications are that UV light may speed polymerization somewhat, it is not a dramatic effect, and not worth obtaining shortwave UV sources for this purpose; just use the sun, which also provides heat and fresh air which seem to be the primary oxidizers.  UV-C falling on some surfaces especially metal screens will create ozone, and it's possible that is the cause of UV having an effect for some and not others (people reporting online).  I did not notice any more ozone than usual - the lamp head is metal and the unit does make a small amount of ozone by itself.

 And this limited effect was using a very nasty, hazardous, UV-C source which most people won't have access to anyhow.  If it's speeding up the polymerization only a little, there is no sense spending $400 on a 100w mercury vapor lamp and ballast.



 ~≈{👁}≈~







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