One of the cool materials at Shapeways is Frosted Ultra Detail. This material prints in layers using a wax support material. If you design the model right some of the wax material can be trapped inside to make interesting effects. This material supports 0.01 mm embossed and engraved resolution which looks great. I redesigned my QR Code Business Card and printed it in Full Color Sandstone and Frosted Ultra Detail. Check it out:
THE secret to frosted ultra detail is to put an exit hole into each internal empty space. When I originally created this card I only placed one exit hole from left to right thinking this would indicate to Shapeways that the empty spaces inside the model should be allowed. NOPE! (Laugh) The maker must include a very small exit hole into each empty space inside the model.
This worked out much better on version 2: