Dear Frank: Don't feel bad about sending so many letters to the list. I love hearing from you and I'm sure others do as well. It's always nice to hear the thoughts of an educated person. Please forgive me if I cc. my answer to your letter to the sundial List. If you have questions, others might have the same.
I think that Americans have the same misconceptions about porcelain too, thinking that porcelain is just for dinnerware or insulators. People don't realize that it can also be fired onto metal (like a bathtub). As I told you at the conference, when it is applied to metal it becomes incredibly strong. I could not believe it when the manufacturer struck a sample with a hammer and it did not even crack! You wrote: "I am starting to settle on the two terms: 1. high-temperature vitreous enameling (porcelain) 2. low-temperature oven-baked enameling (powder coat)" I think that your terminology adequately describes the two types of durable enamel. (the third type of enamel is regular acrylic or oil artist paint applied at room temperature which is not nearly as durable). Just remember that powder coating always involves application by electrostatic attraction. The metal is charged with electricity using an electrical clamp in a special room. (I don't know if it is positively or negatively charged). The paint looks like dust and is oppositely charged so that it is attracted to the metal. After the paint dust is applied, the object is baked in an oven where the dust melts and briefly turns into a liquid and then hardens onto the surface of the metal. If two colors are needed, then separate applications and bakings are required. The first color must be covered with a stencil or masking tape so that it is not covered up by the second color. So you can see why it is difficult to have more than two colors using powder coat. I am sure that this explains why powder coated clock and sundial faces only have two colors. Porcelain glass dust (called "frit") is not applied by electrostatic attraction. It is applied either by hand or by silk-screening techniques. Hope this clears things up. John -----Original Message----- From: Frank King [mailto:[EMAIL PROTECTED] Sent: Wednesday, April 25, 2007 2:34 AM To: John Carmichael Cc: [EMAIL PROTECTED] Subject: Re: Porcelain Sundials Dear John, I write off-list this time, mostly because the list has heard rather a lot from me recently!! Your correspondence has been fascinating. It has taken a while to sort out the different techniques. One reason is that U.S. terminology and English terminologies are a little different. As John Davis has mentioned to me: in England, we think of "porcelain" as referring to tea cups and high-voltage insulators, sometimes also to ornaments made in Germany and elsewhere. To English ears, the term "porcelain dial" sounds as though it is made of ceramic, perhaps made up from tiles. The term "powder coating" is also new to me and I have been trying to find terminology which would be well understood to English manufacturers. I think the word "enamel" would be used for both kinds of technology. I am starting to settle on the two terms: 1. high-temperature vitreous enameling 2. low-temperature oven-baked enameling The first is definitely the more exciting and more durable but limited in size. The second is obviously much cheaper and you can bake a whole car if you want to! I was most interested in your detailed explanations and, especially, that with oven-baked enameling one is limited to two colours. This might explain why most clock dials are just one or two colours in England. The main colour is usually blue but I attach a photograph showing a church clock with a red dial. This is S. Mary's Church, Penzance which is the most southerly and most westerly Town of England which is why you can see a Palm Tree in the foreground. I send this to you not just because of the red dial but because, just to the left of the dial, you can see the top of a pole carrying power lines. You can clearly see the white insulators (one of these is very close to the X for 10 o'clock). This white insulator is made of what we call porcelain! You can see why the idea of a porcelain dial is a little confusing to English diallists!!! By the way, the X and the other Roman numerals are almost certainly gold leaf. Best wishes Frank --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
