Here you can see how much silica I have added to SKRUB. Check out the MSDS of the commercial hard water spot removal products on the market now. Most of them only list the silica content at around 2 to 5 percent. Try to suspend a pen in a cup full of one of them. The complete explanation of how to make SKRUB is in the Product Development Review. It gives a supply for a high quality functionalyzed synthetic silica, an optical grade orange cerium oxide, suspension chem supply, and a hard felt fabrication company.