Set your travel iron to a low temperature setting with the heated surface facing up. Look for a model with a polished steel surface instead of Teflon or other nonstick surface. Weigh down the handle or prop up the sides of the iron to create a stable surface.
Add a few drops of food-safe pigment to the iron's surface and melt a dime sized lump of wax into it, stirring so the two mix together. Create random color patterns and swirls by varying the ratios and lightly mixing in a few different colors.
Set your white poster board on a flat surface with scrap paper under the edges and corners to protect your surface from beeswax.
Smooth your beeswax-loaded iron all over the surface of the poster board in a variety of motions to create different looks. Press and pull straight back for a series of organic looking veins. Use the iron's edge to draw straight lines of wax. Melt away wax that was already applied using the iron's heat.
Add details to your image by adding or removing wax with a heated soldering iron. Play with distance and closely watch the reaction of the wax to this focused heat source.
Seal your completely cooled finished art piece with a clear coat of spray varnish or by framing it under glass. Due to the temperature sensitivity of beeswax you will need to store your painting out of direct sunlight in temperature above freezing and below 120 degrees.