The First picture is before finish is applied. The second picture is after finish, but before any exposure. The Third image is after 2 1/2 months exposure.
The pictures never seem to do the real thing justice, but I hope you can see some of the effects of this study from them. As each sample is slightly different, it is important not to compare each sample to each other, but to the previous pictures of the same sample.
#1 – Combination Polycrylic, UV Resist, Matte finish (2 coats each)
#2 – Matte finish (2 coats)
#3 – UV Resistant clear acrylic coating (2 coats)
#4 – Polyurethane (oil based clear semi gloss, 2 coats)
#5 – Polycrylic (water based clear satin, 2 coats)
#6 – Control Sample (no finish applied)
One thing I wish I had done, looking back now is to have had a second control sample that was not exposed to the sunlight at all, but sample #6 had no finish at all applied to it. This test was conducted indoors; the samples were all on the same piece of wood which was placed in a window (facing south) in my home where it was exposed to sunlight each day, all day.
Results:
As far as UV protection goes, Sample #6 faded more than any of the others, but every sample still had a significant amount of fading. Sample #1 faded the least.
Two coats of each finish were applied, so sample #1 ended up with 6 coats total, #6 had none of course, and the rest had two coats each.
Of course I have not tested all finishes you can use, but I tried to use some of the most common. The purpose was to see if the UV protectant really made any difference compared to other finishes, so it almost didn’t matter which I used. Also this test will continue for at least 6 months to a year longer, and I will add more pictures as I go.
Other than the control sample (#6) which had no protection, and as expected, did the worst with fading, the Matte finish (#2) was second to last in effectiveness and faded almost as bad as the control sample (#6).
In third to last place was the UV coat (#3) which surprised me a little. If it offers any UV protection at all, it isn’t for pyrography.
The top three were the polycrylic (#5), polyurethane (#4), which actually seemed to offer a little UV protection, and #1, which did the best overall. Because of the results of each finish individually, I think I am safe in concluding that the first sample which performed far superior to the others did so because it had 6 coats of finish. The amount of layers of finish seems to have made a bigger difference than what finish I actually used.
Another interesting side note is that of the yellowing, or darkening of the wood. When wood darkens it can certainly exaggerate the effects of fading. It may be hard to tell from the pictures, but the Polycrylic (#5) offered the best results for preventing darkening as far as individual finishes. Once again, Sample #1 performed the best in this area as well. Again, because of the individual results, I can safely conclude that the amount of layers, or coats of finish makes a bigger difference than what finish is used.
Summary:
There doesn’t seem to be a finish of any type that offers any significant amount of protection from the sun for pyrography, even if it has UV protection. What little protection you can get for fading as well as darkening of the wood seems to be accomplished by applying many coats of finish.
It does take prolonged exposure to fade a pyrograph, so working with a piece in sunlight or florescent lighting, or transporting a piece is not enough exposure to effect it a great deal, however I normally still protect a piece from the sun even if I am moving it.
If you are doing something for use outdoors, the biggest challenge is not sunlight, but weathering. If you place a piece in the shade, or facing away from the sun you can avoid fading from UV rays, but weathering will do a lot of damage very quickly. Weather in fact will do a lot more damage than the sun. For outdoor use you will need finishes that are water proof and you will need to purchase a clear finish at a marine shop. (The same finish used for boats.) It is expensive, but will be the only thing that can protect a piece placed outdoors. If it is exposed to direct sunlight, it will still fade.
Time will fade any piece a small amount, but if permanent placement of a pyrograph is not where it will be exposed to direct sunlight, they have been known to last for generations.