They are wonderful for "direct to rubber" techniques.
1. Spray a little water with a fine mist spray bottle or even just drop a few drops of water in with an eyedropper. Mix the water into the paint with your paintbrush. Have several paintbrushes on hand to do this, one for each color you're using.
2. Make sure that your stamp doesn't "resist" the paint. Some stamps, especially the bold ones, resist water-based paints due to a coating on the rubber from manufacturing. If your ink pens or the H2O's tend to bead up on your stamp, just lightly sand the rubber with a fine grit sandpaper (I use 600 grit) and clean the stamp.
3. Paint the H20's onto the rubber. Bold stamps work well, but fine line work well too! If you're quick with your painting and your paint is still wet, stamp immediately. Otherwise, use a fine mist bottle and lightly mist your rubber, then stamp. Mist again, stamp again to get a lighter impression. Do this again to create various depths of image brightness and to create "shadows".
4. Let dry and enjoy!
The Hero Arts real flowers collection works exceptionally well with this method.