We have laser printed on a variety of natural materials including maple, birch, pine, oak, and leather. In each case the natural grain plays a part in the result. This article shows these grain effects and tells how they arise in our process.
Consider this image of Richard P. Feynman on vegetable tanned cow hide:
See the moire-like pattern of white snow on his face? Do you see how the snowflakes are slightly stretched out horizontally? Weird, right? Now take a look at this image of vegetable tanned cow hide showing the grain.
The dark splotches with brown threads are skin cells. The lighter colored space around these is created when the hide is stretched during the tanning process. See how this space is marked by lighter colored bands? This pattern of spots and bands is the “grain” in vegetable tanned cow hide. In our process we've discovered it doesn't darken at the same rate as the skin cells. This causes the bands to remain light colored in the final image. At the scale of this test, 3 in. x 5 in. (8 cm x 13 cm) the banding is pretty disruptive and lends a weird Sci-Fi vibe to the result. On a much larger scale, about 10x maybe, the effect should disappear. You can see this for yourself if you move backward from the screen you're looking at. In small scale the bands occupy a lot of viewing angle. At a much larger scale and from a distance of about 5 ft. (1.5 m) the effect might take on a whole new, and more pleasing, visual esthetic. We haven't done any large scale leather testing yet so that's just a guess. So that's leather grain. What about wood grain?
Maple and birch are very similar woods. They're both very commonly used in pyrography because they yield consistent results when heated. To understand how heating brings out the wood grain in our process consider the following series of three images.
We begin with the original color image of the Teahouse at Koishikawa the Morning After a snowfall by Hokusai.
To make a pyrograph we convert all the colors to shades of grey.
We use a laser to heat each pixel according to its grey value and this is when the magic happens.
We carefully select a section of plywood where we hope the grain will enhance the image we're printing. In this example we centered the large oval in the grain between the teahouse and Mt. Fuji. We thought that the dark-light-dark bands of blue-pink-red in the sky would look best overlaid on this wood grain.
Other grain effects simply appear as if by magic. One example is the extra bird above and to the right of the original three. This was just an unassuming spot of sap when we started that turned out to look like a far away bird partially hidden in cloud. We were also happily surprised when the grain on the snowy roofs suggested gentle pressure ridges in the snow.
Cleaning and Finishing
The final step in the process is to remove as much ash and char as we can without smudging the image. The grey smudge on the leather Feynman is ash. To remove it we blot the work with a damp lint-free cloth. This picks up enough material to create a recognizable negative image but can also leave a residue on the original.
It's much easier to clean maple and birch. We use a combination of compressed air and vacuum to blow and suck away the char and ash. Once it's clean we use Grumbacher Final Fixative to add a colorless, flexible, non-yellowing, and protective satin finish that prevents smudging.