Lightning® silver/gray powder is recommended for use on all glass, metallic, highly-varnished surfaces, hard rubber, safes, blue-steel guns or dark-colored surfaces. Many technicians prefer silver/gray powder due to its high sensitivity for developing latent prints on so many different surfaces. It is necessary to place a lift of a latent print developed with silver/gray powder on a black backing card. We recommended using a different Zephyr® Fiberglass Brush for each color of powder, therefore, if you use black powder have one Zephyr® brush for your jar of black powder and another Zephyr® Fiberglass Brush for your jar of silver/gray powder.