Welcome to the second installment!
I had some pieces of leftover marble from a flooring project the former owner of our house had left behind. Just a word here on minerals and stones. I never buy pre-crushed stones. They are too uniform for my taste. I use a very large granite mortar and pestle to reduce the raw stones and minerals before sifting. I also use bonsai soil screens to sift into six or seven general sizes and hand-pick the pieces I want. For an overview of minerals in the correct range of hardness, visit “http://www.greatsouth.net/”
The picture here shows the mortar and the screens I use, along with a sampling of stones in the shop. The final step is to create a fine dust in the mortar to use as a binder between the larger stones.
Once the inlay is prepared, I typically start experimenting with different stone sizes, mixtures, and patterns. In this case, I already knew I was going to use white marble (with some gray streaks) for the trunks. I also referred to pictures of birches (and walked out to the front yard to look at my river birches) to get an idea of how the branches want to grow out of the trunks. While I didn’t shoot for botanical accuracy by any stretch, I wanted the trees to be recognizable for this piece.
In general, it is best to place the larger pieces the way you want them. Then, fill the voids in-between them with finer and finer grades of stone or even mixtures of different stones to get the effect you want.
Here, I wanted the thinner branches to be a darker brown/black than the white trunks, just like in nature. So, I mixed up several minerals: black mica, anthracite, aragonite, limonite, spar gypsum, and probably a few others I have forgotten. Note that for inlay into wood, you must stay below a hardness of 5 or 6 or the resulting inlay will be too hard to grind and sand flush. This does limit the choices you can incorporate, but there are a number of really beautiful minerals you can choose. Below, you can see the darker mix I used for the thin branches and to fill in between the larger pieces in the trunks. I use artists brushes, dental picks, toothpicks, spoons; any number of things to assist in moving the stones and minerals around.
After the bulk of the stones were in place for the trunks and branches, I laid in the calcite rim in a similar fashion. I use water-thin CA glue to cement the stones in place in any number of steps, depending on the nature of the piece.
Note that the leaves were not inlaid yet. The next step was to start the grinding process. I use an air driven die grinder for the rough grinding, starting with 60 grit, then to 80 grit. Once the high spots were cut down to manageable levels, I began the sanding process using the slower electric sander shown below, getting the surface to about 220 grit.
A few words on safety. You MUST USE A CHEMICAL AND DUST RESPIRATOR WHILE GRINDING AND INCORPORATE SOME TYPE OF DUST COLLECTION!!! A DUST MASK DOES NOT CUT IT!! The minerals and stones often contain toxic substances. For example Malachite is toxic, lapis can be very toxic, and on and on. The dust you will create is extremely fine and will irritate you lungs (at best) or sicken you (at worst) if you don’t take proper precautions. Also, I wear nitrile gloves during grinding for the same reason.
Here is a closeup of the rim area before the first grinding step.
Okay, that’s it for now. I will leave you with a last shot of the piece after the first set of grinding and sanding steps. Still lots of filling in to go!
-- patience is a virtue ... in woodworking, cooking, and life in general