I get this question often so I thought I would address it. "How did you cut that blue stuff to be so perfectly joined into the wood?" That would take some serious skill indeed.
Epoxy resin is actually a 2 part liquid that, when mixed together, forms a hard polymer. The final form of the resin will be clear on its own or can be colored using a dye or pigment (powder). Both dyes and pigments will give different effects.
Whether you're using a dye or pigment, this is usually added after part A and part B of your mixture are sufficiently mixed. As the natural color is clear (or colorless) the amount of coloring solution will determine whether you achieve a translucent or opaque final look. The more dye or pigment added, the closer your table will be to opaque. A little bit goes a long way and doing a test sample is best if you're a newb.
So, as you can imagine pouring a super sticky colored liquid mixture that is moments away from going through a chemical reaction gets dicey. Building a water tight form for your table is paramount. I remember back when I did this for my very first time for my own dining table. I had a leak in the form and stood idly by while I watched hundreds of dollars of resin mixture seep out onto my basement floor. If you have a leak, you're toast (usually)!
My method of building a strong water tight form includes using caulk or silicone inside the joined areas of the form. Once you know you have a strong form, you can place your wood in the form as you like.
Temperature is a key factor as well. Resin likes to go through its chemical reaction at around 65-75 degrees. Too cold and your resin won't harden enough leaving you with a gummy ultra sticky result - not good. Too hot and the resin will cure too fast which could potentially cause it to crack and separate - also not good. There are no ways to fix a bad resin cure!
The first 12 hours are going to be key indicators of a good resin cure but it won't fully cure for 48-72 hours. I usually stick around to babysit my resin pours for about 1-2 hours to ensure no leaks are present to cause a panic. After the 72 hours are up I release the table top from the mold. It might not be pretty. Many times the edges shrink in on themselves or you might have cured resin all over the top of your table.
The final step before the normal sanding process would be to get the table flattened by a large planer. This will rid the table of any excess resin on the surface and plane the wood down to a smooth and flush surface with the resin. After that you're pretty much home free!
Hopefully this helps anyone doing a DIY resin top but if you have questions feel free to comment below.