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 Post subject: Re: Wood cabinet with a campfire smell
PostPosted: May Mon 06, 2019 6:10 am 
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Joined: Apr Sun 08, 2007 6:47 am
Posts: 4465
Location: British Columbia
Superretrodyne wrote:
Jim,

I'm glad to hear that worked well for you. I will try it on a few books.

Arran,

This is a delayed response as I was up in your neighborhood at the Olympic Peninsula with no means of communication. I wasn't expecting the Sitka spruce to be so large.

Shellac is wonderful. I'm sitting at a French polished desk. There is a piece of birdseye maple on the desk I just sprayed a coat of Zinser on for my wife to take a look at for use in the renovated kitchen.

Yes, something may have been done to the case to help it survive. Do you really think the manufacturer was trying to insure it would last for generations? It's just a consumer item. After 80 years, entropy has almost always won. The inside of a case is not finely finished like the outer case. Any shellac coating it was given 80 years ago probably was permeable from the beginning. Temperature and humidity changes, unless it was kept under museum conditions, the shellac insignificant in a few years. Shellac is a technically a thermoplastic, attached to the wood by adhesion. A standard "tape test" on a new shellac surface will probably remove 5% of the finish. Shellac is the most fragile finish. It flakes, and alligators. Humidity, temperature, water, alcohol, pH changes, and many other agents easily breach whatever seal shellac may have originally provided. Most gas penetration is through the end grain, which is generally neglected anyway. Wood structure is like a straw. You can actually blow through a piece of seasoned red oak. Microbial agents work from the inside to deconstruct cell walls in wood. A small drop of water easily tests the permeability of a surface. If it still has surface tension after 5 minutes, the finish is sound. Otherwise, it really provides no protection. There are also several ways the long term life of shellac can be compromised before it is even applied.

An original French polish is the best form of a shellac finish. It takes about 50 coats originally and then must be renewed, frequently, if it as an object that is actually used. Professionally used French violin bows are generally renewed every time they are rehaired, which is at least annually. A luthier who practices French polishing over the original varnish will renew the shellac on every visit. My daughter's 1769 Austrian is redone twice a year. My desk is in need of a going over. I have a massive late 19th century French china cabinet that horribly failed a shipper's version of a tape test. It lost 100% of its finish wherever packing material was taped to it.

So, my advice remains, if it smells, an easy way to hide it is to seal over it.

John


John;
You are really splitting hairs, the point I was trying to make was that the insides of any radio cabinet that I have owned was not raw nor untreated wood, shellac was only one of several coatings that may, or may not have been used on the inside, a dab of alcohol would quickly answer that question. There are also different grades of shellac, different cuts (ratio between pounds of shellac used per gallon of alcohol) and different colours, all with different characteristics. Like for instance, 78 rpm records were often mounded from shellac, they do not often warp, nor do they break down easily, even in humid environments, so clearly the mixture used is a lot more durable then white shellac.
In Zenith cabinets they used a dark blue paint, in RCA sets it was often silver paint, sometimes a dark brown, what the chemical nature was of these is unknown. Hide glue seems a likely candidate for a sealer, it was cheap and readily available in any cabinet shop. Casein was another popular substance used back in those days, along with some early man made substances. Again, the point being is that the insides of the majority of these cabinets was sealed with something, and it does not simply disappear, which means that odors would not necessarily penetrate the wood and could largely be removed by cleaning.
Regards
Arran


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 Post subject: Re: Wood cabinet with a campfire smell
PostPosted: May Mon 06, 2019 6:00 pm 
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Joined: May Wed 23, 2018 6:28 am
Posts: 425
The issue is not whether or not the interior of a cabinet was finished when it was new. All finishes are fragile and, unless taken care of, deteriorate. No one takes care of the inside of the cabinet. There was no reason to take the same amount of care of the inside of the cabinet as the outside, so whatever was done was at most second-rate. Humidity and temperature changes alone will damage a finish after decades, even inside a home. Many old radios spent decades in garages, sheds, barns, and damp basements exposed to a wide range of temperature and humidity.

I mentioned before, I deal with wood that was first finished as early as the renaissance. 80 year old radios are new by comparison. I also worked with an R&D lab for 15 years studying material properties. For the last 15 years most of my work has been on computer models of the deterioration of materials for the DoD and a private international company. In both cases, billions of dollars are at issue. There is an inescapable law of thermodynamics that things, left to themselves, fall apart. The only issue is how long it takes in the environment in which it exists.

Lacquer, shellac, hide glue, and casein on wood all deteriorate in a time span of a decade or two. Lacquer yellows first, then crazes and cracks. Shellac does the same, only more quickly. Hide glue was useful with wood because it dissolves in water, making repairs easy. Casein is the most unreliable of the group because of its chemical properties. It is inherently acidic so it its mixed with lime to attempt to make it neutral. its behavior is affected by salts. I had a set of late 19th century French chairs that had spent years near the French coast and had been in storage. They were made using casein glue. While in storage the moisture softened the casein, which was acidic and ate away at the wood. Every joint was rotted from the inside even though externally the chairs looked fine. If you read about casein, you would discover itis hydrophobic. It has an isoelectric point of 4.6, which is the pH at which it has no free electrons, making it chemically neutral at that pH. This is fairly compatible with the acidity of wood which has a pH range of 4 to 5. Unfortunately hydrophobia disappears in the presence of salt, something that is in the air near the French coast. If the pH of the wood is different than the casein, things fall apart.

Since I don't know what kind of paint was used for the inside of cabinets, I can't say much about their deterioration, but you can read about the issues at this conservation site:

http://wccfa.com/glossary.html

What I can say for sure is that it is unlikely any finish used on the inside of a radio cabinet retains its integrity more than a couple of decades. It may still look OK, but at a microscopic level, it is porous.

John


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