The Care and Feeding of Plastic Radios
My passion is obviously collecting plastic radios. "Plastic" includes many materials, in my case, mostly Bakelite and Plaskon, as well as Styrene and Tenite. Over the past few years, I've had some email discussions with some people knowledgable in the field. With their permission, I've decided to reprint some of those discussions here... at least the answers to my questions, anyway.
This first section is a response from Barry Ornitz to my question regarding the oft-asked-about "Scrubbing Bubbles" test for Bakelite. Barry also discusses the identification, cleaning and preservation of Bakelite and a bit later, and his general recommendations for storage and surface protection
......Dow's "Scrubbing Bubbles" (I think technically known as Basin, Tub and Tile Cleaner) contains a small amount of glycol ethers. These are good solvents and if the surface has any residual phenol, this will dissolve and turn the foam brown colored. However, this is not a very good test. I can think of several types of plastics that could do this. However, it does not hurt the phenolic to use "Scrubbing Bubbles" on it. The phenol it removes should not be there anyway.
Also this test relies on the fact that old phenolic plastic must already be degraded. If the plastic is new, or has been recently cleaned, the test will likely not work. The reason that it works sometimes is that old phenolic plastic parts in radios were never manufactured very well. Bakelite is a CHEAP material, and if the phenol and formaldehyde are not mixed in exactly the right proportions and/or the curing is improperly done, the finished material will be more likely to degrade with age. Properly proportioned and cured, Bakelite degrades very little.
Until thermoset polyester and epoxy resins became available in the 1950's, Bakelite (and closely related melamine resins) were the only thermoset plastics available. Bakelite will not melt if heated, and its odor when heated is extremely distinctive (the phenol). I really do not understand why it is so difficult for people to identify.
The old standby works here: keep in a dry cool place. Lower temperature slows any reaction rate. Since many plastics contain fillers (like sawdust, calcium carbonate, mica, etc.) that can absorb moisture and swell, keeping the plastic dry is a good idea. Naturally you should avoid direct sunlight too because of the ultraviolet present. Indoor lighting is rarely a problem. Very low temperatures can make plastics brittle, and high temperatures can warp them and increase the degradation rate.
Note that electrolytic capacitors require a somewhat humid environment to function properly. Thus you have some conflict with storage conditions. Unless you are keeping a museum collection, a reasonable compromise is to keep your radios in the same environment you are comfortable at. Thus a normal home, with a comfortable temperature and humidity range, is fine. Very low temperatures can make plastics brittle, and high temperatures can warp them and increase the degradation rate.
Celluloid, nitrocellulose, and cellulose acetate have a unique problem with their degradation. They release acid as they decompose which acts as a catalyst for even faster decomposition. These can be stored in a sealed container containing a dessicant like silica gel and zeolite molecular sieves. However, keeping them in open air does almost as well since the acid evaporates and is carried away. As I wrote about earlier, washing and rinsing with baking soda will help protect the surface (but cannot protect deep inside the plastic).
As for wax, I have mixed feelings. Silicone waxes and polishes can do a wonderful job. But if they ever have to be removed, the job is nearly impossible. If you ever feel you might repaint an item, NEVER wax it with silicone waxes. The old standby, Carnuba wax, is much easier to remove in the future. Other vegetable waxes and oils like Lemon Oil are similar. Watch out, however, for the solvents in some liquid waxes. I have known of some that caused stress corrosion cracking of ABS plastics and surface hazing of styrene-based plastics. A wax fills in small scratches and surface blemishes, but because the coating is so thin, it does little chemically to protect the surface below. [Some waxes can give added ultraviolet protection, but this is mainly for automobile paints.] A wax can help in keeping dust from scratching the surface when the dust is wiped off.
The only other thing I can think of is keeping the surfaces clean. Some skin oils can gradually be absorbed in plastics leading to discoloration when the oils oxidize.
Looking over what I wrote, it appears that to summarize the recommendations is to just use good common sense. If only more people getting into radio restoration would do this instead of looking for magic cures and no-effort cleaners!
This next section is part of a discussion I had with Mike Shultz when he responded to a newsgroup query I posted about straightening a Plaskon radio dial bezel. I found it enlightening and well worth posting here.
......I am not familiar with this Tesla radio. I am wondering, however, whether the bezel you refer to is actually Plaskon. Plaskon was not generally used for this application. What I suspect your bezel is made of is "Tenite". This type of plastic was used extensively for bezels, grills, pushbuttons and knobs, and occasionally for complete radio cabinets. Tenite is much softer than Plaskon and is thermoplastic, which means that it softens when heated. Plaskon is thermosetting, which means that it hardens when heated (during the curing phase after the piece was molded). Tenite is frequently marbleized, and is notorious for its habit of warping, shrinking, and generally falling apart. Certain kinds of fungus love to grow on it and sometimes it gets a nasty vomit-like smell. Plaskon almost never warps.
So, if your bezel is Tenite, you might have a chance of unwarping it. Looking at my trusty plastics reference book, for Tenite (which is Cellulose Acetate), this plastic was molded at a temperature of about 350-400 degrees F. and it will exhibit significant softening at about 120-200 degrees F. This is why Tenite radio cabinets are often badly melted just above the output and rectifier tubes.
So let me say this: It seems like it should be possible to straighten a bezel by heating the piece in hot water. Depending on the nature of the warp, it might be possible to heat just the affected section, or the entire piece. I would think the best way would be to make a jig which will hold the piece in the desired shape while it is heated and then cooled. I have never done this however on an actual complete radio piece. But I had a junk piece of Tenite (a grill bar) which I experimented with. I simply held it in running hot tap water until it reached the temperature of the water, then physically bent it, and held it in the new shape and let it cool. It did, indeed, assume that new shape. I would be hesitant about trying it with an actual, irreplaceable radio part for fear of making the situation worse.
By the way, Tenite also absorbs water, so don't let it soak for any length of time! An oven in which the temperature can be accurately controlled would be better than hot water, but they are harder to come by. You might also want to wait until you can find some scrap material on which to practice, like an old junker pushbutton Philco with the Tenite bezel (the ones for which they are now making repro's as seen in ARC).
So, I hope this information helps.
Thank you to Barry and Mike. I am interested in collecting more information about plastics used in radio cabinets. If you have something to share, please email me and I'll be happy to post it here.
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