Crushed Lapis Lazuli Inlay Ring

I took a piece of lapis lazuli, smashed it into gravel and dust, and packed it into the channel of a stainless steel grooved core ring blank. Thin CA glue wicks down through the stone and locks every grain in place. After it cured hard I put it on the lathe and sanded through the grits from 80 all the way to 1500, then polished it until the blue came alive. The pyrite flecks in the lapis end up looking like gold dust scattered through a deep blue night sky, and no two rings ever come out the same.

Lapis lazuli is a deep-blue metamorphic rock made of multiple minerals (Lazurite: Makes up the main blue color. Pyrite: Forms shiny golden flecks and spots. Calcite: Creates white veins or patches. Diopside: Contains trace amounts of iron or chromium that turn it a vivid green or yellowish-green hue.)

This is a great first inlay project. The stainless core does all the structural work, so you are really just filling a channel and then sanding carefully. If you can be patient at the sanding stage, you will end up with something that looks like it cost a whole lot more than it did.

Materials

1. Stainless steel grooved core inlay ring blank, in your size. Get the comfort fit style if you have the choice.
2. Lapis lazuli rough. You do not need much. A single tumbled stone or a small chunk of rough will do several rings. Better grade lapis means deeper blue, less grey calcite, and nice pyrite flecks.
3. CA Glue
4. Thin CA glue (superglue). This is the important one, it needs to be thin so it wicks through the packed stone.
5. Medium CA glue for building up the last layer.
6. CA accelerator. Optional, and use it sparingly, more on that later.
7. Painters tape to keep CA glue from the inner ring

Tools

1. Lathe. I used mine with a ring mandrel. A drill press or even hand sanding will work, it just takes longer.
2. Hammer and a steel plate, or a mortar and pestle.
3. A heavy freezer bag or a scrap of leather or canvas to contain the stone while you crush it.
4. Kitchen strainer, tea strainer, or a set of small sieves for grading the crushed stone.
5. Small plastic container or pill cup to hold each grade.
6. Sandpaper from 80 through 1500 grit. Wet or dry paper is best.
7. Plastic polish or micromesh pads for the final polish.
8. Toothpick, dental pick, or small screwdriver for packing.

Safety

1. Respirator or a good dust mask. Crushed stone means silica dust and you do not want that in your lungs.
2. Eye protection, both for crushing and for the lathe.
3. Ventilation for the CA fumes. They will find your eyes.
4. Never wear gloves, loose sleeves, or a ring on your hand while running the lathe.
5. Do not let CA glue soak into a cotton glove or a cotton rag. It reacts and gets hot enough to burn you.

Wrap your lapis in a heavy freezer bag or a folded piece of leather, set it on a steel plate or anvil, and hit it. Start with firm taps rather than one big swing, otherwise you will send chips across the shop.

You want to keep hitting until you have a mix of everything from small chunks down to fine powder. Do not try to make it uniform. The variety is what makes the inlay look good.

Tip: the bag also stops you from losing material. Every crumb counts.

Run the crushed stone through a strainer to separate it into rough grades. I keep three cups going:

1. Coarse: the visible chunks. This is what people will actually see in the finished ring.
2. Medium: sand sized grains that fill the spaces between the chunks.
3. Fine powder: the dust. This is your grout. It fills the last of the gaps so you do not end up with pinholes.

Do not throw the powder away. It is the single most useful grade you have.

Wipe the channel out with alcohol or acetone to get rid of any oil from the factory or from your fingers. CA will not bond to a greasy surface.

Scuff the inside of the channel with a bit of 80 grit so the glue has some tooth to grab. You only need to dull the shine.

Run a strip of painter's tape around the inside of the ring to keep glue off the inner surface. It saves a lot of cleanup later.

This is a dry pack method and it gives far better results than trying to mix stone and glue into a paste.

Sprinkle a layer of coarse chunks into the channel and press them down with a toothpick. Work your way around the ring and try to get even coverage. Then sprinkle medium grains over the top and tap the ring so they settle into the gaps. Finish with a dusting of powder and press everything down firmly.

Now wick in thin CA glue. Touch the tip to the packed stone and let capillary action pull it down through the layer. You will see the stone darken as the glue travels. Keep going around until the whole layer is wet through.

Tip: resist the urge to flood it. Too much glue at once creates heat and cloudiness. Several light passes beat one heavy one.

Let it set. I prefer to let it cure on its own for a few minutes rather than hitting it with accelerator, because accelerator can leave a white frosted look inside the inlay that you cannot sand out.

Repeat the pack and glue cycle. Coarse, medium, powder, thin CA, let it set, repeat.

Keep going until the inlay sits slightly above the steel rails on either side of the channel. You want it proud, because the sanding is going to take that extra material away and you need somewhere to sand down to. If you finish level with the rails you will sand straight through into the low spots.

For the very last layer I switch to medium CA, which sits on the surface rather than soaking straight in and gives me a solid cap to level off.

Let It Cure Properly

Walk away. Give it a full day if you can.

CA feels hard within minutes but it keeps curing for hours underneath. If you start sanding too early the inlay will smear and gum up your paper, and you will find soft spots that crumble out. This is the step where impatience costs you the whole ring, so go do something else.

Mount the ring on a ring mandrel and get it running true. Moderate speed. Dust mask on, glasses on.

Start at 80 grit and take the high spots down. The goal here is purely to get the inlay level with the steel rails, nothing more. Move the paper side to side so you are not cutting a groove in one spot, and keep checking with your fingertip. When you can run a finger across the ring and feel no step between the stone and the steel, you are done with 80.

Go easy near the end. Once you reach the steel rails they will start to slow your cutting down and act as a natural guide, but it is still possible to dish the inlay if you lean into one spot.

Now it is just patience. I went 80, 120, 220, 320, 400, 600, 800, 1000, 1200, 1500.

Two rules make this go well:

1. Do not skip grits. Each one is only there to remove the scratches from the one before it. Skip a step and you will still be looking at 220 grit scratches at 1500, wondering why it will not shine.
2. Clean between grits. Wipe the ring and your hands. One stray coarse grain dragged along at 800 will put a scratch across the whole thing.

From 400 up I wet sand with a little water on the paper. It keeps the dust down, stops the paper clogging, and most importantly keeps the heat out of the CA. Hot CA gets soft and smears instead of cutting.

A good habit is to sand in one direction at each grit, then change direction at the next. When all the scratches running the old way are gone, that grit is finished.

By 1500 the ring should already have a soft satin glow and you should be able to see the pyrite clearly.

Voids

Now that the surface is level you will see them: little pinholes and pits where air was trapped between grains. Every crushed stone inlay has some.

Wick thin CA into every hole you can find. If a pit is big, sprinkle a pinch of your fine powder into it first so you are filling it with stone rather than a puddle of clear glue, which will show up as a glassy spot later.

Let it cure, then sand back to level with 120 or 220 grit and look again. I usually do this twice. It is tedious and it is also the difference between a decent ring and a great one.

Polish

Take it up with plastic polish or micromesh. I work the polish in with the lathe running slow and light pressure, then buff it out with a clean cloth.

Watch the heat again. Leaning on a buffing wheel will haze the CA and can even soften it. Light touch, keep moving.

This is the payoff step. The dull grey blue turns deep and saturated, the calcite veins show up as pale clouds, and the pyrite starts throwing little gold sparks every time the ring moves.

Peel the tape out of the inside and scrape away any CA that snuck past it. A dental pick and a bit of 400 grit wrapped around a dowel will clean up the inner surface.

Give the steel rails a final polish, wash the ring, dry it, and try it on. The inlay sits inside the channel so the size has not changed.

Care notes: CA is tough but it is not indestructible. Keep the ring away from acetone, nail polish remover, and long soaks in hot water. Take it off before heavy work. If it ever dulls after a few years, a quick pass with polish brings it right back.

1. Pack the stone tighter than you think you need to. Nearly every void I had to chase later came from a spot I packed lazily.
2. Save the powder. It is the difference between a solid inlay and a swiss cheese one.
3. Go slow with accelerator, or skip it entirely on the layers that will be visible.
4. The 80 grit stage feels like the important one but it is really the 400 to 1500 range that decides how the ring looks.
5. Lapis varies a lot. If your stone has heavy grey calcite, sort the greyest chunks out and keep them for the bottom layers where they will get sanded away or hidden.

This same method works with just about any stone, or with turquoise, malachite, shell, or even crushed glass. Once you have done one you will start looking at every rock you pass differently.

Thanks for reading. If you make one, I would love to see how it turns out in the comments