As a lot of people don't seem to realise the purpose of these wonderful artifacts I thought i might write a quick guide to try to make them more popular.
Aquadomes can be won from events(usually with a chess piece already inside them) or bought from the Flaundins, if you have the required amount of reputation.
Flaundin page on the mentor info site
From my experience most people who get Aquadomes win them from events with chess pieces inside them and then try to sell them.
If you try to sell them you get a message stating that you cannot proceed with the trade as the item can only be traded for a similar item. Meaning that you have to trade one aquadome for another aquadome of the same type.
Most people also don't realise that if they take the chess piece out of the aquadome, the chess piece becomes an unencased chess piece in their inventory, and the aquadome becomes weightless AND is reusable. In fact, Aquadomes have unlimited use! You can put any piece of the correct level in and out of the dome as many times as you like.
Trading domes:
When it comes to trading, both parties MUST have the SAME level aquadome, meaning that if you have a HOME Aquadome, one person can have a Jasper rook, and the other can have a Mahogany pawn, and they can trade.
TAX is still the same as if it was an encased piece, so quite high. One person may have a less valuable piece than the other so may ask the other person to add some gold, which is perfectly acceptable, however if you are wanting to trade 2 pieces for one piece you will find that this is impossible, so having spare pawns to trade is the only way, sadly you still get taxed.
I am hoping this has cleared up the confusion people have over the aquadomes, caused partly from the original translation when they first appeared on the .com server, and the fact that most people who own them won them with a chess piece already inside them so didn't see the aquadomes description.