As an eyeglass restoration facility, we see eyewear from the truly antique Civil war era, to the vintage classics of the 1920s & 1930s and on to the pre-war and post-war classics. Plastic, and the restoration of plastic is an art form in and of itself. There are more than a dozen “plastics” that have been used over the decades, and they differ tremendously in their characteristics and problems.
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Your specific question regarding the “white” patches on plastic can originate in a half a dozen different manners, each of which can fortunately be restored, but you must know what you are working with and how to fix it. Testing chemicals are available, but are impractical and dangerous for the one-time owner-user.
Let us simplify our range and begin with the pre-war plastic frames. Prior to polymer plastics, like nylon, the pre-war frames were predominantly Catlin or Bakelite, which were the “new” synthetic alternatives to celluloid, an organic material used to make movie film. To tell them apart you would take a clean white cloth, spray a small amount of 409 cleaner on the frame, and rub it against the cloth. If there is no reaction, it is Catlin…if there is a yellow reaction, it is Bakelite.
The white patches are typically a result of the salt in perspiration leeching out the transient dyes used in Bakelite. This can be re-dyed using a matching dye such as some of those used on shoe leather, but pre-testing for compatibility is a must. All dyes are carried in a vehicle. All vehicles are potentially solvents of your eyeglass frame.
In the case of Catlin, the color is embedded in the matrix of the material, and the “white ” patch is usually the thin surface color sheet wearing through to the base color underneath. These are best touched up with a surface color of acrylic enamel, followed by a clear coat to match the surface sheen. In all cases, the vehicle that carries the dye or the finish coat must be tested in a small obscure spot to determine if the chemistry will adversely effect the frame body.
Keep in mind that many plastic frames were clear-coated with a finishing coating that may be the origin of the white patches you see as the top coat succumbs to UV and body acids. These are generalities, and manufacturing variants will not always fall in these two categories. The post war plastics are far more varied, but again, the first thing to determine is whether the base material is colored all the way through, or if the surface skin is the color, and it has worn through.
A common post war classic example is the Bausch & Lomb Ray Ban Wayfarer. This is a cast colored plastic that tends to get white patches where perspiration salt leeches the color out of the plastic in the area of the temple arm interior flanks towards the tips. This can be restored by dying and surface coating. All the previous warnings apply.
If the frame is post war and is a base neutral color like tan or grey, and then shrunk wrapped with surface color or patterns like leopard or tortoise, you then must use an acrylic enamel to mimic the original color or pattern, followed by a non-interacting clear coat. Clear coats can dry matte, satin or gloss, and will return a uniform surface patina to the frame as well as protecting it from further salt bleaching.
If a collector is determined to enhance their treasures themselves, try experimenting with broken or partial frames that can be found and purchased for little or nothing at flea markets. Cleans used on the frame should never be ammoniated or chlorinated. A baby shampoo is surprisingly effective for cleaning both the frames and lenses, and does not have the solvents or chemicals that can frost certain lenses.
However, in sunglass lenses, the coatings are thin films and should never be exposed to any cleaner in undiluted strength. Eyeglass lens cleaner is another safe liquid to use on both the frame and the lenses, together with a soft cloth. A few lessons with the materials and techniques will go a long way towards your restoration efforts for enhancing your favorite pair. However, if you invest a good deal of money in a truly unique and rare eyeglass frame, you should at least seek an opinion and estimate from a professional before risking damage that can not be undone.
In conclusion we suggest that you establish a good working relationship with a frame restorer wherein you communicate your expectations and intended usage for your frame, as well as acknowledging that you are prepared to invest an appropriate amount of funds per frame to purchase the time and skill the restorer brings to returning your frame to its former appearance. Ask the restorer if they have worked on this particular material and era of eyeglass frame before. Experience is the best assurance you can obtain towards a successful outcome that will allow you to enjoy your wearable art.
-A. Cornell at FRAMEFIXERS.COM Eyeglass Repair. 1-866-372-6339