Alabaster on the Lathe

An ordinary woodturning lathe can be used to cut and polish alabaster until it glows with translucent colors. The author's red and pink vase on the right is 10 in. tall and the small pink vase is 2 in. in diameter.

Turning rocks is tricky, but that just adds to the fun. And delicately colored stones like alabaster, when turned, develop a pleasant translucent glow. I conduct turning workshops across the country and have been impressed at the popularity of alabaster work. I suppose that's not too surprising considering turners are such an adventurous lot, eager to chuck on anything from a worn-eaten tree trunk to a variety of fruits and vegetables. In addition , you don't need any special equipment for alabaster, nor and special techniques. The process is just like scraping out a wood bowl, only slower, although alabaster does have a couple of personality quirks. It's not so much that the material is contrary as that it is different and takes a little getting used to.

Alabaster is crystalline form of gypsum (calcium sulfate), which is the main ingredient in Sheetrock. Gypsum rates a #2 on one commonly used hardness scale (talc being #1 and diamond #10).You might notice some variation in hardness from piece to piece, but even though it's rock, all alabaster is soft. Impurities are responsible for its subtle colors, which can range from translucent white through pinks, to browns, grays and greens. The turned pieces are a bit like crystal wine gasses - lovely, but if you drop one, that's that.

You can rough out the alabaster blanks with any variable-speed reciprocating saw and a large-tooth or bimetal blade. A bandsaw running bimetal skip-tooth blades at slow speeds will cut alabaster. The low-tech chisel-and-mallet approach also works fine. Currently, I'm mounting the rock on the lathe and using an air chisel to knock off enough material to balance the piece, then using a narrow scraper known as a Stewart Slicer (available from Dennis Stewart, 2502 N.W. 4th Ave. Hillsboro, Oreg. 97124; 503-640-3089).

For the actual turning, I use carbiade-tipped scrapers. Commercially available woodturning tools are fine, but I made my scrapers by unbrazing carbide tips from old router bits, then rebrazing them onto square-stock steel (available from KBC Tools, 6300 18-MIle Road,

Sterling Heights, Mich. 48078; 800-521-1740, or 800-482-1047 in Michigan). You can order tools specially made for alabaster from Jerry Glaser, 8341 Delgamy Ave. Playa del Rey, Calif. 90293. I sharpen my carbide tips with a 120-grit silicon carbide (greenstone) wheel.

High-speed steel scrapers are best for the finishing cuts (see top, right photo on the next page). The steel edges aren't as durable as carbide, but they produce a cleaner cut, probably because they can be sharpened to a finer edge. I grind the ends square with no bevel. This way I can use one side until it is dull, then flip it over and use the other side. These high-speed steel scrapers are available from Craft Supplies USA, 1287 E. 1120 S., Provo Utah 84601; (801) 373-0917. Craft Supplies also sells double-faced tape, the type of pin chuck I use (the version included with combination or six-in-one chucks) and Hot Stuff cyanoacrylate glue, which is invaluable for holding the work together.

Alabaster can be crumbly because of fractures and stresses within the stone, so it can break easily on the lathe. I turn each bowl as thin as I dare, usually about 1/8 in. to 3/16 in. My current success rate is about 80% and would be even lower if it were not for the cyanoacrylate glue. Once the outside is roughed to shape, use thin "original" Hot Stuff on anything that even looks like a fracture in the stone. If the glue soaks into the crack, I go over it with the thicker "Super T" Hot Stuff and then spray on the Hot Stuff Accelerator, which speeds glue hardening. If the glue doesn't seem to flow into the crack at all, I assume the crack just looks like a fracture. I repeat this procedure whenever I get nervous about things breaking, usually on the inside when the piece is about 1/4 in. thick and always just before the final thickness.

Safety hazards - Be aware: There is always a chance that block will shatter. Even if everything is going well, dust is a problem. Alabaster dust is similar to Sheetrock dust, so wear a dust mask or a respirator,

A pin chuck, fit into a center hole drilled in the rim side, holds the blank.

The blank can be rough cut round with a reciprocating saw.

Initial scraping with carbide-tipped tools brings the stone into rough shape. Here, the bottom of the bowl is being trimmed flat with a high-speed steel scraper

Above: To center and clamp the preturned wood base to the piece, the author uses a stub with the proper Morse taper for the tailstock on one end and threads for a faceplate on the other. The base is then glued to the stone using the tailstock as a centering clamp. Wooden rim segments are applied with cyanoacrylate glue.

Below: Turning procedures are much the same as for scraping cuts in wood.
 
 

use a dust collector and if possible, work outside. I use a Makita 410 dust collector, with its intake nozzle mounted near the tool rest. This clears the air and helps keep the dust out of the headstock bearings. In addition to breathing problems, the dust can dry out your skin severely, so I wear latex gloves. Of course, wear a face shield: These are rocks, not wood chips, that will be flying off the lathe. I recommend steel-toe shoes, because the rocks are quite a bit heavier than wood, and if you turn enough of them, you will inevitably drop one off the lathe. The last time this happened to me, the 105-LB. piece hit the floor and rolled through the wall.

Attaching alabaster to the lathe - I usually start with a pin chuck from the rim side, then proceed as shown in the photos on the facing page. The only unusual gadget I use is a device to center and clamp the preturned wood base to the piece. It is a simple stub with the proper Morse taper for the tailstock on one end and threads for a faceplate on the other end. With the bowl on the headstock and the base on the faceplate, I screw the base/faceplate assembly onto the stub, insert the stub into the tailstock, then wind the tailstock out until the base and bowl connect. This avoids turning a mortise and tenon to center the bowl on the base.

You can also adapt other chucking systems to alabaster. You can grind a flat on what will be the base of the piece with a belt sander, glue on a preturned wood base, glue or, for small pieces, double-tape a waste block to this base and screw a faceplate to the waste block. Or, you can grind a flat on the rim side, tape it to a faceplate, turn the outside, then glue on a base and waste block as before. Use whichever method seems most comfortable to you.

Turning techniques - You must rely on a fairly gentle touch as you turn, because alabaster isn't flexible. The rotational energy of the lathe must be absorbed by the tool, the tool rest and your hands, or by the scraping away of the stone's surface. Too much pressure or a slip with the scraper either stops the lathe, knocks the piece off the faceplate or breaks the stone.

You will likely find two additional crystals in alabaster: quartz and selenite. Quartz crystals are very hard and may be as large as a pencil eraser or as small as a grain of sand. You will feel them and hear them; they will take the edge right off your tool, sometimes making sparks as they do so. If you run into quartz, stop and dig it out. My "quartz digger" is simply a concrete nail with a piece of wood for a handle. Selenite is another crystalline form of gypsum. It usually is found on the outside of the rocks and looks similar to mica. You can cut selenite, and if it runs deep in to the rock, it can yield spectacular results. But, selenite crystals usually separate from the rest of the piece, so keep filling with Hot Stuff as you turn, as this will sometimes keep the crystals in place.

If you decide to permanently attach a wood base or rim to the alabaster, the Hot Stuff glue makes a good permanent bond. Whenever one of my joints has failed there has always been a layer of alabaster left attached to the wood, indicating the stone, not the glue, as the weak link. Just remember: The wood will move as its moisture content changes; the stone will not. With wood pieces as small as the rims on these bowls, wood movement doesn't seem a problem; with the larger pieces, it can be. After the piece is turned, finish all surfaces of the base with a moisture-sealing finish.

Finishing alabaster - I first sand the surface with 36 grit for rougher shaping, working up through 15-micron sandpaper (available from The Luthier's Mercantile, Box 774 412 Moore Lane, Healdsburg, Calif. 95488; 707-433-1823) for that final glow. I use all the sandpaper dry. My favorite finish is paste wax, but you might prefer lacquer or the traditional oil finishes commonly applied to wood turnings.

Finding alabaster

I get most of my stone from Colorado Alabaster Supply, 1507 N. College, Ft. Collins Colo. 80524; (303) 221-0723. Stan Jones, the owner, says that the company deals mostly be the ton, and small pieces suitable for turning are, in effect, waste that may or may not be available at any given time. You may have to wait six weeks to two months for delivery of a small order. Typical cost is as low as 30¢ to 35¢ per pound, with a nominal handling charge.

I suggest you start with a 20-lb. to 30-lb. block, which in my experience, would be large enough for a 6-in. by 2-in. bowl. Drill cores of 2 in. to 3 1/2 in. in diameter are sometimes available, too. Here again, if you want 500 lbs. of cores, Jones will be happy to core out as many rocks as necessary; if you want 10 lbs. and he is out, the order might take a while.

A speedier yet more expensive route is to order from a specialty supplier. Sculpture House (30 E.30th St. New york N.Y. 10016; 212-679-7474 has alabaster (mostly imported Italian) for immediate shipment and will help you figure out what to order ever the phone. Cost is $1.50 per pound, and the minimum order is $50.

You might be able to obtain the rock from local sculptors or sculpture-supply houses as well: Alabaster is a very popular carving stone. Here in the West, you can often find alabaster at rock shops along the highway. If they don't have it, they probably know who does.

Another approach is to become a prospector. which gets you the best prices of all, usually free. Look for places on the map with names like Alabaster, Gypsum or Plasterville. Gypsum, the main component of Sheetrock, is fairly common, and where there is gypsum there will be alabaster. By asking around, you can usually get permission to dig it. The question is whether or not it will be solid enough and large enough to be useful. Here's how to test: You want a piece that gives off a good ring when struck. Pick the piece up and give it a sharp tap. (My favorite tapper is a wooden-handle rigging axe, which is a framing hammer that combines a typical hammerhead with a hatchet face instead of a claw.) A solid piece will have a clear clink or a ring. If you get the sound of an indistinct "thud," look for fractures and break off anything that looks loose, or try holding the piece differently, then tap again. this is easy for a 20-lb. rock. With a 150-lb. rock, however, it is more of a problem; still you can usually balance it on a corner and get a ring. With a 500-lb. rock, good luck! -M.K.

One final caution about finishes: Your bowls must be purely decorative or at least reserved for the storage of dry goods, because alabaster dissolves in water. How quickly? Well, a few drops of water on a waxed alabaster surface probably won't make marks, but I once filled a bowl with water and the liquid noticeably etched the surface in half an hour. Obviously, if there is a fracture in the piece where water can seep through, things will only get worse. To avoid this kind of damage, I sometimes lacquer the inside surface, especially on enclosed shapes. I don't especially like the look or feel of the lacquer, but it is hard to see inside these enclosed vessels anyway. I also think that with enclosed shapes it is more likely that someone down the line will l put water in them. In those cases, lacquering should work fine, unless a possible natural fracture in the stone eventually causes the lacquer to check.

One of the best rules when beginning to work with alabaster is that if at first you don't succeed, keep trying. As I mentioned earlier, about 20% of my starts are failures, but in the beginning, they were more like 40%. Half of these are due to excessive concentrations of quartz or structural problems with the stone, and half are just my mistakes. Have fun: After all, that's the ultimate point of it all.