wrote:
Hi!

Well, we haven't decided yet for how long the paint should stay as we
are still playing with the idea. Actually, information aout all the
types mentioned would be interesting:

1. What if the paint should stay on the trees as long as possible?
And
if this is not a good idea, how long would other paint stay on before
being washed away? (Rain washing of paint from tree - nature cleaning
human traces?)

Bark being the way it is, you'd probably find that, even if you used
children's poster paint, a lot of it would stay there for maybe years.
Looking absolutely revolting. And that kind of paint doesn't cover
well: it's designed for paper, not non-absorbent surfaces, and it would
be very difficult, if not impossible, to achieve an intense effect.
Old-fashioned whitewash would do it, and can be coloured. But you'd
still have your guilt mocking you from the crevices years later.

Don't use emulsion, though: once it dries, it isn't water-soluble.

2. We actually only thought about painting the trunk, but if
someboday
knows about a paint that can be applied to the leafs too, why not? In
this context the paint should probably stay on as long as the tree
has
leaves... around 6 months?

You risk killing the tree if you paint its leaves: they are its
life-support, and excluding light and blocking the pores would stop
them working. It wouldn't be feasible, anyhow, except with a powerful
spray and a hell of a lot of paint.
[=2E..]

You could get hold of some logs and try it out first. If you want your
paint to be washed off by rain, you'd have to set the logs up somewhere
outside; and even then it wouldn't be a scientific test, as a log
doesn't have the shelter a living trunk gets from the branches and
leaves.

What about _wrapping_ the tree with coloured paper or plastic?

Of course, the students would learn quite a bit from having to _make_
trees with chicken-wire and papier mach=E9: a tree is a subtle piece of
natural engineering, and it could be good to discover how it holds up.

-- =20
Mike.