Both dichroic and iridescent finishes are very thin metal sprays on top of a sheet of glass. They are very easily etched off with standard etching cream. All you need to do is apply a resist over top of the dichroic that you want to remain in place. Typically the resist will have a design cut into it. Apply a liberal amount of etching cream with a clean, new flux brush onto the exposed section of glass. Wear safety glasses, rubber gloves, and have an apron on to protect yourself and your clothing from the acid in the cream. Let it sit for about 15 minutes, then wash off under water at the sink. Remove the resist and you are finished! The resist can be masking tape, scotch tape, duct tape, Mosaic Mount, or even children's vinyl stickers. You could also try using a Sharpie to draw on the Dichroic glass, and apply the etching cream around the lines.
Basic Supplies: Rubber Gloves, Paper punches, resist, Iridescent glass, etching cream, burnishing tool, safety glasses.
Applying the resist to the glass making sure there are no air bubbles underneath the resist.
Applying the etching cream to the exposed glass.
The etching cream has been removed from the two pieces of glass on the left, but is still on the larger piece of glass on the right.
Etch All and Amour Etch are two common brands of etching cream. Note the piece of resist on the right with the dragonfly shape punched out of it by a Paper Punch. Punches like this can be found in Scrapbooking stores, or some office or craft stores.