Opaque Stamp Pads Opaque stamp pads are used by industries requiring special purpose opaque inks (thick and viscous or pigmented) for marking nonporous surfaces. These pads are supplied in pairs so that the two surfaces can be inked, then rubbed together for uniform distribution of the ink. By rubbing the two sides together thicker inks can be applied without clumping. This allows for clear, legible impressions over time. Opaque pads are made of fine cloth covering hard felt attached to a wood base. Standard size #1 is 2" X 3". Other sizes available.