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Organic Coatings:

This is an area where advances are being made every day. The titanium and stainless tributes really need no protective coating since these metals are self healing and the oxides do not alter the metal’s color nor are they affected by UV or environmentally corrosive chemicals. The only issue we discovered with these metal coatings is their propensity to scratch. We perform an extreme scratch test using a needle. Even the protective barrier coatings will scratch. The common denominator, at this time, with all organic coatings is that failure is predicted when exposed to the elements. It may take 20 or 30 years, but they will fail.

Indoor Display:

If the tribute is to be displayed indoors it really needs no coating, especially if it's framed under glass. That's recommended to guard against finger prints or someone accidentally using an abrasive cleaner or a gritty cloth to clean the tribute. Anything will scratch, including diamond under the right circumstances!

If the tribute is mounted on granite and framed without glass we recommend our standard coating, a clear fluoropolyurethane (FPU). You’re probably familiar with this member of the fluoropolymer family - DuPont Teflon®. Fluoropolyurethane is one of the finest coatings available in the world. This coating, which has been engineered to withstand the outdoor elements for 20-30 years, will protect your tribute from finger prints and scratching. It does not yellow when exposed to UV.

Exterior Display:

Many manufacturers of bronze plaques, one being a very large producer, are using acrylic lacquer to protect the metal from discoloring oxidation. These coatings are being used on plaques destined for outdoor display. The following quote is from the automobile coating experts at Trinity 1945 Inc. Lacquers were used extensively on cars in the past.

“Acrylic lacquer paints have been largely discontinued by most manufacturers. Acrylic Lacquer auto paint is primarily for antique or classic car restorations, where the highest possible gloss and shine is desired. Acrylic Lacquer auto paints also will not have the durability of acrylic enamels or urethane auto paints. For this reason, we recommend the Acrylic Lacquer paints for garage kept vehicles that see limited use. Our Acrylic enamel auto paints, will have more durability than the Acrylic Lacquers, and will have a slightly less glossy finish. Please also note that buffing out the finished paint job when using Acrylic Lacquer auto paints is required.”

In addition, manufacturers have strayed from lacquers because of the toxicity of chemicals used in the compounds and MSDS toxic chemical regulations. Lacquers cannot stand up to the severe conditions.

Some manufacturers are using a clear, baked on coating, probably a powder coat. These coatings are hard and tough, but they're still organic. They have a tendency to yellow, and they cannot be reapplied in the field once failure occurs. In addition, some manufacturers who offer etched stainless recommend using no coating if exterior use for long duration is anticipated. This will hasten the demise of the paint or dye they use to get the image contrast. Once the color disappears the image will still be there, but observers will just have a very difficult time seeing it.

The best coating option would bond on a molecular level with the metal’s surface and be inorganic. There are only a few clear coatings I know of that meet these specifications. Unfortunately, most are what they call micro-coatings. They are extremely thin, so they appear to scratch. What is actually happening when a needle is used in a scratch test is the metal is indented. That appears as a scratch. All other coatings are organic or a hybrid combination which means they will eventually degrade.

Inorganic Coatings

Outdoor Display & Jewelry:

There is a hi-tech alternative available. We located a company that can deposit a clear, inorganic coating via a special process. This clear coating bonds on a molecular level with the atoms on the metal’s surface. Since these coatings are inorganic and inert they are not susceptible to microbial attack or environmentally corrosive chemicals. They are also extremely hard. To give you an example. The Vickers (HV) hardness of 316L stainless steel is 152. The hardness test for sprayed coatings, like the clear polyurethane on an automobile or the fluoropolyurethane we use, uses the pencil scale. For example, a catalyzed acrylic polyurethane has a pencil hardness of 2H. A catalyzed modified acrylic polyurethane may have a 4H hardness. Our fluoropolyurethane has a 6H hardness. In other words, sprayed coatings like urethanes are relatively soft compared to PVD coatings.

The Vickers hardness test is one that measures the hardness of metals and hard coatings. The Vickers (HV) hardness of diamond, the hardest surface known, is 816. One DLC clear coating has a Vickers (HV) hardness around 306. It is twice as hard as the 316L stainless itself. It is a very hard and practically indestructible coating, especially when used on a piece for exterior display purposes. The draw back is that one off pieces are very expensive to coat.

The ultimate coating would be a synthetic diamond. This coating has all the properties of real diamond including a Vicker (HV) hardness of 816. We are working with a laboratory on a synthetic diamond coating. If this coating, which interacts with the surface on a molecular level, works on our metals, it will be the coating of choice for outdoor environments. It is totally inorganic and impervious to microbial attack. The process is, however, very expensive and to date is only available as a micro-coating.

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