We took a big live edge cookie (aka round slab, from a horizontal slice of a tree), power carved out the middle, and poured resin into it to make it look like a geode! Here are the materials and tools we used:

Arbortech Mini Grinder: http://bit.ly/2pWDzPu
Arbortech TURBO Plane: http://bit.ly/2pX09Ym
Arbortech Contour Sander: http://bit.ly/2pXxkew
Total Boat epoxy kit w/ pumps (slow) https://amzn.to/2CJcjN3
Total Boat varnish https://amzn.to/2CJrZ2I
ISOtunes, our fave hearing protection: https://amzn.to/2OVwtWx
Powdered pigments https://amzn.to/2OtZziH
Alcohol inks https://amzn.to/2OxOcGw
Big crystals https://amzn.to/2pDWr64
Small crystals https://amzn.to/2Pfrn7M
Metal table legs https://low.es/2RQ6WQi
Spray paint for legs https://low.es/2OoNDzD
White fine glitter https://amzn.to/2NkBRAW
Cordless sanders https://low.es/2RIU5zz
Plastic drop cloths https://amzn.to/2Ou00tl
Tiny cups for mixing https://amzn.to/2DPpvkD
Big stirring sticks https://amzn.to/2xVfnSi
Small stirring sticks https://amzn.to/2xToe6H
Propane torch https://amzn.to/2O0Tjzu
48” level https://amzn.to/2EnZ9qe
Hot glue gun https://amzn.to/2C0iQBB
Foil tape (for the hole) https://amzn.to/2R7psT7
Sheathing tape (for the underside) https://amzn.to/2PMmraF

Step 1: Prep the Cookie

You may be able to find a slab or a cookie that is already flattened and ready to go, or you might be using this technique on some already processed lumber, but for us the first step was to prepare our cookie. We had hoped to use our X-Carve CNC to flatten it but it was too tall, so instead we used a router sled. There are a lot of tutorials out there to make your own, but we used one that a friend had. It's essentially two wood boards that act as rails on either side of the piece you're flattening, and another board that your router nests into that rests across the two rails. You slowly go back and forth with the router, eating away a small amount of material each time you make a complete pass over the whole thing. Eventually, all unevenness is flattened out and it's parallel with the surface your rails are sitting on. The most important things to keep in mind are making sure your rails are parallel. For a cookie this size, this took us between 4 and 5 hours - it's a very slow process!

After flattening it, we removed the burn marks left by the router by sanding them down, and we chipped off the bark with chisels.

Step 2: Cut a Hole Through the Center

Alright, after spending hours getting a perfect surface on your cookie it's time to mess it up! There are two parts to power carving the cookie to get it ready for resin. First we're gonna cut a hole through the middle, and next we'll carve a recessed area. For both, we decided to use the rings of the tree as outlines for our cuts. For the center hole we traced the ring we wanted to use (maybe 5-6" across in diameter) and we used a hole saw to punch out a circle in the center.

Next we used the Arbortech Mini Grinder to cut from the hole to the edge our our outline, working from the center outwards. You can be really precise with the tool and sneak up to the line, but it also eats away material really fast.

Step 3: Carve Recessed Area for Resin

Next we used another tree ring to figure out where we wanted the resin geode to be. We marked it with a white pencil and carved about 1/4" down using the Arbortech TURBO Plane. The way this tool works is it carves on the bottom of the wheel, but not on the sides of the wheel, so once we got our recess started we could make it deeper without having to be as careful about accidentally making it wider. You could also use a router for this part.

It doesn't have to be perrrrrfectly flat and smooth (the tool leaves some texture after all) because the epoxy will self-level when you pour it, but you do want to make sure it's generally level so that when you pour, the epoxy stays about where you put it and doesn't slide to a section that's lower.

Step 4: Resin Pour!

To prep, we used foil tape (because it's stiff) to tape up the inside of the hole so that resin didn't pour down into it and we used sheathing tape (because it doesn't leave residue) to tape the underside of the cookie so that resin didn't soak through the cracks and glue it to the board we were resting it on.

For pouring the resin itself, there's not technical "wrong way" to do it but here are some tips we found to make it look like a geode.

Use a combination of pigments and alcohol inks. Mix the pigments directly with resin in individual cups (so you have a cup for each color). These will give you most of the color you end up seeing in the final piece, and are great because you have more control about where the color is placed. You can also mix multiple pigments into one cup to make your own color. We drop alcohol inks on top and they create the awesome little "cells" of color that really make the resin look like stone. It's harder to control what they're gonna do, and a little goes a long way.
Overall, stick with a limited color palette and look up photos of real geodes for inspiration.
When you're pouring your cups of colored resin, we like to generally do it in rings for this look. We pour in rings until the entire surface is covered, then we blend it with the heat gun aiming from the center outward.
For the first round of pouring, we do a lot of heat gun blending, but then we do less and less as we continue to add more and more details.
You can add glitter to your resin, sprinkle tiny crystals into your resin pour area, move it around with a stirring stick to create different designs... there's a lot you can do!
When you're done, give any areas where you see bubbles a quick zap with a blowtorch to pop them

Overall, this step is a LOT easier to get a feel for by watching the video than just reading tips, so we'd highly recommend watching it, then doing some smaller practice pours (you can just do it over a piece of scrap wood with foil tape on the sides) so that you can get some practice in.

Step 5: Crystal Center

After your resin is fully cured, remove the tape from the center hole and sand off any spots where you may have accidentally dripped resin on the wood outside of the pour area. Then, it's time to do the crystal center. We started by painting the wood with acrylic paint so that when we glue crystals onto it, the color we painted shows through instead of dark wood showing through. This really helps with the illusion of the piece being a geode all the way through.

We did a gradient, starting with a warm white at the top (that matched the color at the center of our pour/edge of the hole) and then faded it to a light teal that complimented the colors in the pour. We also tried throwing some glitter on the wet paint but I'm not sure that did anything haha.

Then we hot glued crystals to the inside, starting with the biggest ones at the bottom and smallest ones at the top. The hot glue is surprisingly sturdy, though we'll reinforce it later. This part is very meticulous and takes a long time but is also very satisfying. When I started doing the smallest of crystals at the top, they were too tiny to hold with my fingers so I used tweezers, and putting a dab of hot glue at the end of the tweezers made it way easier to grip the crystals without them slipping around.

Step 6: Final Clear Coat and Edges

Next we did a final clear coat of epoxy over the entire thing. Our center pour hadn't been perfectly level so one side was a little high, and because epoxy is thick the clear coat 100% masked it. When pouring, we made sure to drip it all over the crystal center to reinforce the crystals, and we just let it drip over the edges. We used the heat gun to spread it around.

For the edges, we finished them in varnish that had the same high gloss sheen as the epoxy. so it blended with the epoxy drips. But it's a lot thinner to apply so it was easier to manage than the epoxy, which worked well for the sides. We also used it to touch up a couple areas on the top where the epoxy had completely soaked into the wood and hadn't left a glossy finish. We did 2 coats of varnish on the sides.

In the comments on the video, a lot of people suggested adding a coat of varnish to the underside too, which we didn't do in the video but plan on doing thanks to their suggestions!

Step 7: Legs

We used metal legs we found at Lowe's, but really you could use anything here. You could make your own, you could use hairpin legs, etc. We cleaned ours with acetone, gave them a light scuffing with a sanding pad, then spray painted them with satin black paint+primer in one. When they were dry, we screwed them to the underside and then we were done!