Hello Steve,
Consider translucence, the diffusion of light on the substrate. This
semi-transparency diffuses the contrast between light and shadow. Plastic,
glass even rock can be translucent and compromise the shadow on a surface.
I have noticed this problem with high quality Carrara marble, smoky glass,
porcelain and plastic slabs. An opaque, non-reflective surface like grey
oolitic limestone is best.
Colour is just a distraction. The contrasts of shades of grey from bright
sunlight to dark shadows are our medium.
Roger Bailey
Walking Shadow Designs
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From: "Steve Lelievre" <steve.lelievre.can...@gmail.com>
Sent: Friday, February 24, 2017 10:04 AM
To: <sundial@uni-koeln.de>
Subject: Dial face colouration
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. I need something in between: light enough to catch a shadow, but
dark enough to avoid glare in full sun. I assume that latitude has a
bearing on this, as the midday sun illuminates more strongly as we
approach the equator. In my case, the design latitude is around 45 N. My
dial will be about 25cm in diameter.
Are there any conventions or empirical guidelines, or even practical
experience, to help me choose?
Which properties matter? I quick read of Wikipedia suggests colours seem
to involve hue, saturation or luminosity (or parallel concepts in other
classifications).
Cheers,
Steve
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