I sandblast bricks for fundraisers, blast portraits in gray granite and tan limestone. I want to move into the 21st century and laser etch these items in a similar fashion. I would like to do this without the paint-on material, such as Cermark or Thermark. What type and wattage laser would it take to darken the stone and brick. I have just started my quest and would appreciate any help you could give me. Thanks, glad I found this site. Alan O.