This is a rack for use while etching circuit boards.I had just been laying the boards in the tank but I wanted to be able to etch multiple boards and to use a bubbler to increase the speed I was etching and so this rack was born.The large slot underneath is for three aquarium stones.Personally I do not use Ferric Chloride as it is a very nasty chemical that is toxic and difficult to dispose of. I use Ammonium Persulphate instead. Its just as cheap and available and comes in a powder so it has an indefinate shelf life. Disposal is as simple as flushing it down the drain. I have recently been evaporating off the water and it leaves behind pretty blue crystals.Print on a big printer like a Prusa or other Reprap printer.Place 3 Aquaculture Aquarium Stones from Walmart underneath in their slots. Length is up to you but this object is designed to so I can print 2 of them and use on 10 inch stones.Connect air pumpFill tank with etchantPlace circuit board on edge in slotsStart air flowAs mentioned above I recommend using Ammonium Persulphate as an etchant. It is MUCH safer to use, is a lot less toxic, and is very thin so shouldn't interfere with the stones. Ammonium Persulphate comes as a powder and is mixed with water. Unlike Ferric Chloride it maintains its low viscosity and has the consistency of water. It also will not stain anything.