I´m a stone sculptor from Portugal and I work with wood and metal, but mainly with stone, as my country has a rich tradition of working with marble, granite and other types of stone.
As a part of my daily routine, I search the internet trying to find tutorials about marble carving by hand and with power tools, but there are very few, and usually directed more toward architecture than to sculpture. So I decided to enter this contest to show that stone is not boring and that it can mirror the beautiful colors of the rainbow, as if it died the ground were it land (everything you see is usually black, white or grey like in tombstones). Also, because it will be the first marble work tutorial on instructables. Gluing pebbles doesn´t count as stone work and if you search marble, well, the result is marbles! Enough said and let´s start. This project is not very hard, expensive or messy as you would see. But its stone, so expect some resistance of the material. The secret is to insist until the job is done. We will try to make a marble table lamp by piling up marble discs of various colors.

Here´s what you´ll need:

Supplies

An electric drill
1/8" and 1/2" drill bits
Diamond cup saw with 2" diameter for the drill. I chose a saw with center guide to make the hole for the wire.
Colored scrap marble pieces. You can find some on the road or fields and near construction sites. You can also ask for samples on a vendor of construction materials or stones or someone who works with stone for graveyards or fireplaces. I just bought 3 square feet of marble scrap in a store for 12 euros. They even let me choose the pieces! As the stones don´t seem very colorful when dry, I normally wet them to see what they will look like when polished. That´s why I always carry a tiny water spray bottle wherever I go. Some of the stones weren´t easy to find, especially purple and blue, in this case, bluish. I saw some nice Brazilian blue granite on one store, but I don´t think granite would go well with the marbles and limestones I´m using.
Parts from an old table lamp I had around the house. It´s mainly a metal plate with a 1/2" hole in the center for the base. 1/2" diameter threaded lamp tube with some nuts to attach the base. I also bought a black lampshade.
Electrical wiring components: wire, switch, plug, bulb and socket
1 tube of Araldite or other epoxy glue 3 sheets of wet sandpaper grits 100 300 600
Spray lacquer or any kind of floor wax
A piece of dense styrofoam to serve as a base for drilling
Water hose
Bucket with water
In terms of safety there´s really not much to care about. For example you don´t need a respirator mask as everything is done under water. Ear protection is advisable only if you´re going to use the drill in hammer position.

Step 1: Drilling

Prepare your workspace. There should be a hose nearby and maybe a drain to get rid of the water and stone slurry, or you could just dip the stone in a bucket with water enough to cover the stone and drill it in there. Using the second method the water will get muddy with stone dust and it will be harder to see how the drilling process goes.
Put the slab of stone on top of the styrofoam and the hose over the slab with water running. The water stream should be enough to clean the slurry generated by drilling, but not too much, or it will splash around which is not very advisable because water can get inside the drill engine and cause an electrical shock. The piece of styrofoam is used so the drills can come out on the bottom without much resistance. Start by drilling a guide hole with the 1/8" drill bit in a place of the slab that can accommodate the larger 2" hole we will make with the cup saw. If you use the hammer position on the drill remember to turn it off near the end to minimize crumbling the stone too much on the way out.

Drill a larger hole with the 1/2" drill bit. Try to keep the drill perpendicular to the slab to make a straight hole.

Attach the cup saw to the drill and insert the drill bit guide on the hole you made before on the stone and start drilling. Again, it´s critical to try and keep the drill as straight as possible so you don´t warp the circles you´re making. If you can drill with a drill guide or stand it will save you time later when leveling the surface. You can use a piece of wood with a hole the same diameter as the saw to help guide it. I´m using plastic bags to protect my shoes from the spilling water.

As you drill you´ll find that some stones are much harder than others, some crumble easily, others seem to take forever to drill. Even in the same piece of stone you´ll find hard and softer spots. Be patient.

Step 2: Gluing (or Not)

I started to drill the 7 discs of stone. Then I piled them to decide where the colors will go, it helps getting the stone wet on this step. I mounted the lamp base and start inserting the marble discs in the tube where the wire goes. I like to use epoxy glue to secure the discs of stone to the tube, but you can leave them unglued so they can rotate. I usually use a good epoxy as I have had bad experiences in the past with cheaper brands.

As soon as the epoxy has cured for 24 hours you can start leveling the surface of the cylinder with coarse wet sand paper mounted on a piece of wood or rubber. If you choose to not glue the pieces you will have to sand them one by one and they will not line up so perfectly. If there are any pieces of stone protruding too much, you can knock them down with a rasp, the kind that´s used for wood. This will also help levelling the cilinder.

Step 3: Sanding

If you don´t want to start the sanding process by hand, you can buy some sanding discs for the drill to start sanding the marks of the cup saw on the stone. Also flap sanding discs and a grinder will make the job go faster, but unless you have some experience working with stone you risk taking out too much material on softer zones. That´s why I prefer to do it by hand.
As happens with other materials you should start wet sanding with a coarser grit like 80 or 100 and then use finer grit until you achieve the desired level of polishing. Usually if I want to make a near mirror like finish I go to 2500 grit, always in increments, so the finer grit will remove the scratches made by the coarser grit used before. You can start sanding dry and then move to wet sandpaper because, unlike wood if you don´t sand stone with water the scratches will never go away. Also you need to continually rinse the stone with water while you sand so you don´t get scratches from floating stone particles.

Once in a while dry the stone cylinder to check for bumps, depressions and scratches.
Change sandpaper grit for a finer one as soon as it starts slipping on the surface. Try to sand as evenly as you can. if you stay toomuch time in one place you´ll start creating flat planes. As soon as you use the 500 grit paper the stone will start to be very similar in look when wet or dry. When you reach an amount of glossiness you´re happy with its time to apply the finishing.

Step 4: Finishing

My preferred method for finishing a marble piece is sanding it till 2500 grit. The level of glossiness attained is just wonderful and there´s almost no need to seal it (depending on the type of stone. Some are not polishable). As I usually don´t like to spend much time sanding (none of us do!) I go to 500 or 600 grit and stop there. Then I apply some kind of fake gloss or matte finish, depending on the look i´m pursuing. Clear wax used on ceramic floors work well, just be careful because some of them have a yellow hue which will change the color of the stone. The same applies to lacquer. The clearer, the better. You can apply liquid wax with a brush or a piece of cloth . I decided to leave the stone with all its natural cracks, holes and crystals.

Step 5: Final Assembly

Besides gluing the stone disks to the tube I decided to also glue the stone cylinder to the lamp base to make it sturdier Then I just connected all electrical wiring and voilá! A rainbow marble table lamp.