It's a rainbow made with a printed holder, vinyl tubing, food coloring, and silicone sealant. The OpenSCAD file is parametric so you can use different tubing diameters and the depth of the holes. It will also spit out the theoretical lengths of tubing needed for each band. The pictured printed part is big enough that I had curling with PLA, kinda motivating me to upgrade to heated bed.(1) Print the holder.(2) Cut tubing to lengths indicated in the text output of the OpenSCAD script. Better to err on the side of cutting too long a piece.(3) Insert the smallest piece into the holder. If it seems too long snip off little bits at a time until it looks right to you. Then insert the next largest tube. Make sure its top is flush with that of the smaller tube. If it is not cut off a little at a time until it is. Continue until all the empty tubes are inserted.(4) Filling the tubes: I tried many sealing methods. The easiest I have found so far is to use a hot glue gun to make a plug on one side, fill, and make a plug on the other side. If using thin tubes like in those pictured, you may have some difficulty filling the closed tube. The 'trick' is to not drop in enough liquid at once to block the entire cross section of the tube. If you do surface tension will hold the bead of water in the tube and you'll need to flick the tube to break it up. Getting zero bubbles when you plug the 2nd side requires a little technique. What worked best for me is trying to extrude the almost into a tube wall, so it would flow around the sides leaving room for air to escape until the last possible moment. Even if you get a few bubbles, you can trap them at the base of the rainbow afterwards by holding it upside down and flicking the offending tube.DISCLAIMER: By building this rainbow you agree to not hold Trevor Law liable for anything bad that happens to you. I was somewhat wary of using hot glue on PVC tubing because toxic gases can be released, but I asked my engineering technology teacher and he said it's probably okay as long as it is only heated for short time. I felt it was an acceptable risk for me but I provide no guarantees that step 4 here is safe or healthy. I highly recommend you wear goggles or other eye protection while applying the hot glue. When the glue is applied on the second side to close off the tube, it is substantially hotter than the boiling point of the water it comes into contact with. Although I didn't have any issues with this at the time of this writing, it does sizzle and spattering of hot glue/water/pvc is possible.(5) Insert the tubes back into the holder. Then look at it for awhile. If you are building this and want more detail on something, please drop a comment.