Just like any oxidizer, if too much is used it can create a grainy effect. If you want to achieve more contrast, I suggest using the sodium platinum solution (available at Bostick & Sullivan, Santa Fe, NM) rather than the potassium platinum. In my work, I use palladium predominately, and use the platinum as the contrast agent, the 1 1/2% H2O2 is to keep the print free from chemical fog, which is what will happen if no restrainer is used at all. Some of my prints are pure palladium, and if you ever want to experience the true beauty of this medium, pure palladium is absolutely exquisite.