For my acryilc students I bought a pack of about 50 picnic styrofoam
plates...and actually have the kids was the plates off carefully with
sponges when done. Usually will last an entire quarter.
What also has worked nicely is buying a roll of freezer wrap paper, and I'll
have kids tape the paper shiny side up.
I especially like using the freezer wrap for tempera paint...where I have
kids put about a nickel sized amount of paint out, the colors along the top
edge. This I have them use like watercolor, reaching up and pulling color
down to mix on the freezer wrap.
If I have another class coming in that will paint, the neat thing about the
freezer wrap is that you can have the kids use a sponge or paper towel, and
just wipe the freezer wrap off...leaving it taped down to the desks then it
is all set for the next class. Works sweet!
When painting outdoors...I want the kids to use wood palettes. The warmth
of the wood to mix paint on has a use many do not consider and that is that
the wood is warm in mood and temperature. It doesn't require much warmth in
the color to appear warm against the white of a white palette..yet when
looking at the color of nature's light that comes off bright, students
(adults and teens) will be challenged to mix pigment that can match.
By having a warm wooden palette...the artist naturally mixes the color even
warmer which is a better match for nature. This is because a warm color
that looks quite warm against a white palette (white being cold in nature)
looks not quite as warm on the wood palette. Thus, the painter mixes the
color warmer to appear the warm s/he wants on the warm palette. This means
that the color is being applied warmer to the painting itself and requires
less tweaking later on or adjustments. You see the color and its
temperature more accurately from the beginning.