Hello Karson,
UV degradation and protection is a very complex subject that eliminates insomnia for most folks. A few of us, myself included, find the topic interesting, but then I love reading chemistry textbooks in the middle of the night and learning about various fungi and their effect on wood, so go figure…
I've used Penofin products in the past and they performed well. I'm not sure which version you are referring to (Blue label?) I've only used the Ultra Premium Red label, but the two are similar. Penofin in the blue label uses Transoxide pigments for its UV protection. I've been experimenting with manufactured UV resistant finishes, as well as making my own UV resistant finishes for about 10 years, so I know a wee bit about the subject. There are two schools of thought about how to reduce UV degradation… This is somewhat "deep", so please bear with me…
The use of UV stabilizers in manufactured finishing products works well, to a point. There is a ton of chemistry involved in determining the right type and amount of UV inhibitor to use. To complicate matters further, various types of UV inhibitors are available, each with their own particular drawbacks.
Two primary methods have been adopted to stabilize light/UV light: 1.) Competitive UV absorption by UV absorbers in the 290-350nm wavelength range and 2.) Trapping of the radicals formed during polymer degradation by radical scavengers using Hindered Amine Light Stabilizers (HALS). The two primary systems employed to reduce UV degradation are chemical and pigmented.
Chemical: Ciba Speciality Chemicals has a HALS stabilizer, which is a liquid amine stabilizer. It consists of an almost pure mixture of Bis (1,2,2,6,6-penatamethyl-4 -piperidinyl) sebacate and Methyl (1,2,2,6,6-penatamethyl-4 -piperidinyl) sebacate. It is used in automotive coatings, wood stains and industrial coatings and is a clear chemical liquid. It is VERY expensive. My research and testing indicates that these types of chemical stabilizers have great resistance to UV degradation initially, but tend to loose some of their effectiveness over long periods of time.
Pigmented: Pigments will prevent the UV from attacking both the coating system and the substrate. The best type is the old Zinc Oxide and the newer Titanium Oxide, which forms a complete block out. Other pigments of course will provide similar protection, but will obscure the grain. The Transparent Iron Oxides and Titanium Oxides have a very fine particle size and are therefore, transparent. The Titanium Oxides are also used in pharmaceutical formulations and are very expensive.
Transparent Iron Oxides are cheaper, but they are colored. However, the color can be used to enhance the surface of the timber. Since they are nearly clear, they do not obscure the grain. All UV systems protect both the coating and the surface that the coating is applied to, the substrate. However, in deciding which system to employ, one must consider the properties of the coating itself. Is it a varnish film on the surface, or a penetrating finish?
Thick finishes with UV protection (like marine varnish), do not really penetrate the wood surface deeply. Therefore, a breakdown of the coating allows deterioration of the wood surface, by allowing moisture to get under the coating. This delaminates the remainder of the finish. The penetrating oil type of finish (like Penofin) has the advantage of soaking into the wood and does not form a skin to lift. The varnish finish has certain advantages however, because the film thickness that penetrating oil finishes provide is substantially less than multiple coats of varnish.
The Oxides being inert, do not lose their effectiveness over time (vs. the chemicals), but if the surface coating deteriorates, the UV factor is decreased. So, it is a bit of a trade off, if the coating breaks down, the UV light will get through. Penetrating type coatings offer less breakdown of the surface coating, but do not provide as thick a surface film layer. So you can see that it is a long road to hoe, no matter which system you choose.
I have experimented quite a bit with blended finishes, in an attempt to strike a balance between the better overall coverage of the chemical systems and the superior long term performance of the pigmented systems. I have achieved excellent results with several protocols, but I think I could spend the rest of my life looking for the perfect UV resistant finish and probably only come close to that goal.
Since I fund experiments like these out of my back pocket, it can be a challenge to continue experimenting when the cost is so high for the stabilizers. However, it's in my nature to explore the "why" and "how" of things… It's as natural as breathing to me, so I continue experimenting… The results of my experiments over the last twelve years have allowed me to substantially improve my overall finishing protocols. My thin film polymerization testing was a real eye opener several years ago and the results of that testing have helped me for many years to produce better and longer lasting finishes on my turnings.
I try (as best as possible and within reason) to apply established scientific testing protocols when testing finishes in my studio. It has become a large part of my non-turning related testing and research and working under privacy agreements, has grown into me assisting some finish manufacturers with improving their existing products, as well as being in on the development and testing of other finishes before they are sold.
Looking back, I would have never guessed that this would be a part of my studio's work, but it's stimulating for me, as this is an area that I enjoy and have a strong passion about. If can help you again, please do not hesitate to contact me. Take care and all the best to you and yours!
P.S. It looks like I've given another $5.00 answer, when you probably only wanted the 5-cent one… Please accept my apologies in advance!
Steve Russell
EWW, WVP, EWWFS
The Woodlands, Texas