I often find myself biting my tongue when looking at glass images of Silver Birch, or Aspen trees, created in glass. All too often, the artist has simply cut strips of white glass, and painted a few horizontal lines on them, and plopped them down onto a background. They look like white ladders, frankly, dodgy ones, and not the least bit like nicely observed, natural-looking tree trunks...they have no personality, no character, and look stiff and unrealistic. These two sketches show what I mean:
Often, light gives us a sense of "form" - the roundness of the trunk, as it illuminates one side, and casts a shadow on the other. But there are times when the light is subtle, and there is no obvious shadow. Then, we need to use the information provided by the bark. And the rules of perspective.
PERSPECTIVE FOR CYLINDRICAL FORMS.
At our eye level, horizontal marks on trees will be horizontal. As we look DOWN toward the roots, the marks will "dip", and as we look up towards the sky, the marks will appear to arc upwards. This is a rule of perspective. It will be very obvious when you are close to a tree; much less obvious from further away. You can prove this to yourself with a drinking glass or even better, a cardboard tube. Hold the top rim at eye level. It will be straight. Lift the glass/tube, and look UP at the rim. It curves upwards. Drop the glass/tube, and look DOWN at the rim. It will curve/dip downwards.
Have a look at the images below, they show what I mean: