We must be careful when we use the term "enamel". As I mentioned before, it can refer to regular artist paints, oven baked paint or kiln-fired porcelain. Porcelain is a vitreous enamel which means that it is composed of glass frit (fine dust sized particles of glass). It requires HIGH firing temperatures of about 1500 degrees F. and kiln-type ovens. But the enamel and powder coatings used on car parts or lawn furniture is more like traditional paint and is baked at much lower temperatures- about 350 degrees F. if I remember correctly.
Porcelain high temp kiln ovens are usually smaller than low temp paint enamel ovens which can be walk-in size. Perhaps the large blue dials on St Margaret of Antioch's Church are made from low temp paint enamels and not porcelain. This would explain the problem of oven size. Or, they could have been made of porcelain in smaller sections as John Davis suggested. I'd love to find out if they are of real porcelain or just paint enamel. Besides having greater durability (Porcelain might last 500 years? Most powder coats are only guaranteed for 10-20 years), there is another huge advantage in using porcelain instead of baked painted enamels or powder coats. FULL COLOR! Porcelain designs can be of any number of colors and can even have color gradations because it can be silk-screened using the 3-color photographic technique. (Yellow, cyan & magenta and black) Just like a color photograph. Porcelain can be applied by a machine and multiple copies can be made. You can not do this easily with powder coat or paint enamels, I was told. To get multiple colors and colors gradations with low temp paint enamels they must be hand-painted. Stencils are difficult to work with and don't give you color gradations. And it is almost impossible to use more than two colors using powder coat because of the difficulty in masking. So, if you want multiple and blended colors of photo quality designs, then you should use porcelain. (Silk-screened or hand painted with multiple firings) Now here's a thought- All over England I saw the clock faces on all the churches have only TWO colors (either black and gold or blue and gold). This leads me to believe that these clock faces might be made of low temp baked paint enamels and not porcelain. Does anybody know exactly what the English clock faces are made of? Whatever it is it seems to work since most of the clocks look pretty good. The company that makes the clock faces might be able to make two-color sundial faces if provided with the design. If you're interested in the details, this is how they made my porcelain dial faces: It was easy for me to be a porcelain customer. I just emailed the manufacturer a hi res PDF of a colored design that I made with Delta Cad and Photoshop Elements, and his machines applied and duplicated all the colors exactly. I also sent him a separate PDF CAD drawing showing the location of the gnomon attachment holes and disk size. They cut out the metal disk so that it was the right size and shape, and they cut out the gnomon attachment holes with computer guided laser using my pattern. Then they baked on a background color (white) on both the front and back sides of the disk. This encases and protects both sides of the metal from rust and the elements and prevents warping of the disk that would result if only one side of the disk were covered. Then they silk-screen on the three primary colors and black. I swear that the porcelain looked as good the paper printout from my computer! John Carmichael . -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Patrick Powers Sent: Monday, April 23, 2007 4:03 AM To: 'Sundial List' Subject: Re: Porcelain Sundials Message text written by Frank King >John Carmichael explained that the biggest oven that his suppliers use will accommodate a maximum size dial of 46" square. The Margaret of Antioch dials are over twice that size. I wonder whether Brookbrae could still do a job that big. If so, they may have a customer!< I don't know. There have been changes at Brookbrae over the years. Earlier in this thread John Davis referred to an enameller that he used and I seem to remember that it used them at least partially because they were one of only a few who could accommodate the size of dial that he then had in mind. I am sure that he will read this and will explain the issues. I am actually unsure of the needs of the technology here because the problem is supposed to be the paucity of ovens of a size that can take the metal bases. However in a very extended restoration of a vintage car (it's 42 years since I last drove it!! ), some years ago I needed to get some replacement mudguards repainted. I then discovered that the originals had been stove enameled and in trying to be authentic I have found no difficulty in getting that done first with a matt-grey priming enameled layer and later with a gloss one. Are the ovens used for stove enameling car parts (the ovens I used for my mudguards were of a walk-in size) the same sort as those used for artistic and enameled signs etc? I have heard that stove enameling needs a higher temperature than powder coating It would be nice to know if a combination of the two technologies can be used to solve the problem you have. Patrick --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
