On Fri, Feb 24, 2017 at 1:04 PM, Steve Lelievre < [email protected]> wrote:
> Fellow sundiallers, > > I’m planning to make my next sundial from outdoor grade UV resistant > plastic sheeting. These come in a range of colours and I want to choose one > that works well for a sundial. Assuming I get the material grit-blasted or > somehow treated so that it not shiny, and leaving aesthetic considerations > aside, what light-related attributes should I be looking for? > > As anyone who has played with paper sundials knows, a white surface is > hard to look at in full sun, even if non-shiny; black would not show any > shadow. Well, one would have to try it to be sure. Maybe black would work, because nothing is *completely* absorbent. So why not start with the least reflective color, black. ...and then try something else if the shadow isn't visible. I've never made a durable waterproof, windproof fixed-mounted outdoor sundial, and so I'm just guessing, not speaking from experience. I made a few pocket tablet-dials. My first one was typewriter-paper (computer-paper now) on corrugated cardboard. Too bright to look at, of course. So, for the rest of them, I got some brown construction-paper, but, instead of using it, I just drew the hour-lines on the brown corrugated cardboard, instead of pasting paper to it. I, too, would be interested in hearing about the conventions, empirical guidelines, or practical experience. I probably would have asked that question sooner or later. Yes, I've heard the color-attributes referred to as hue, saturation, and brilliance. I'm sure that luminosity means the same as brilliance. Maybe "brilliance" is better, because it doesn't carry any implication of the object being a *source*. I'm sure that brilliance is important, and probably is the most important attribute. It seems to me that I once read that brown is a low-brilliance orange-yellow mix. Hue could matter if some hues, wavelengths, are more damaging, irritating or annoying than others. Of course the lower the saturation, the more grayish, the more nearly the reflected light is an equal mixture of the visible-light wavelengths. So, if some hues are more desirable than others, then low saturation, grayish-ness, wouldn't serve any purpose. We hear that, among the visible colors, blue is less desirable to look at a lot of. Maybe partly because of its own effect, and partly because it's nearer to the uv end of the spectrum. Yellow is the complement of blue. And red and orange are at the opposite end of the visible spectrum from blue. So, low brilliance, probably preferably high saturation (less grayish), yellow orange or red? I think that means brown, but it was a long time ago when I read about it. If trying brown, might as well start with dark brown. If brown isn't available, then maybe dark tan. If that isn't available, then maybe dark red or dark orange (or maybe "dark orange" is the same as brown or tan)? I don't claim to have the answer to that question--just a few guesses. No doubt someone will be able to genuinely answer the question. Will this be a horizontal sundial, or a higher-mounted sundial intended to be visible from farther away, for visibility to neighbors or passers-by who aren't near enough to look down at it? The translucency of the materials you speak of could be helpful if it's to be viewed at a distance, because a translucent flat dial can be read from all directions; and, if it has a gnomon on each side, then it has a shadow regardless of which side of it the sun is on. An equatorial flat dial has the advantage that its construction-principle is the most immediately-obvious to all neighbors and passers-by. Unless translucent, of course it's only readable from one side during either particular half of the year. Next easiest to explain the construction of, is the horizontal-dial. Has shadow all day, all year, and readable from all directions if you're standing near enough to it. But maybe not everyone is that near to it. And, after that, the easiest to explain the construction of are the the flat dials whose dial-plate-normal (perpendicular line) is in the plane of the meridian: That's a south-facing vertical dial, or a south-facing reclining dial. (But if the necessary visibility-direction called for it, I suppose it could be a fairly-nearly-horizontal north-facing reclining dial too, though it of course wouldn't have as much coverage of hours and seasons.) If you want the construction to be easily-explained to people, then you wouldn't use a declining, or reclining-declining dial. But of course sometimes visibility-direction requirements could make one necessary, especially with non-translucent, non-transparent dial-face material. All this from someone who has never built a durable, waterproof, windproof, fixed-mounted outdoor sundial :^) There are a lot of questions that I'd ask about that. I'll save those for another post, sometime. Well, one question now: Were pillar-dials, the ones at street-intersections or town-squares, always aligned with the cardinal directions? Doing so would mean that the shadow-casting edge, for the east and west faces, would be parallel to the dial-face, reducing the hour-coverage for those faces. So did they sometimes make it a declining dial, so that the shadow-casting edge would intersect the dial surface, on all four faces? I've considered eventually, when I get around to it, making a pillar-dial mounted on a lamp-post. It would be in the form of a hinged wooden box, a cube-dial without the top and bottom faces, with holes in the top & bottom, and hinged to close onto the lamp-post. The inside edge of the holes in the top & bottom would be rubber-lined, for squeezing onto the lamp-post without damaging it, when closing the box onto the lamp-post. There would be a bolt-and-wingnut on the corner-edge opposite the hinge, to tighten the hinged box onto the lamp-post. I'd consider declining-dials on the four faces, to that the shadow-casting edge would intersect the dial-face, on all four faces. Were pillar-dials usually, often, or ever made that way? Michael Ossipoff > >
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