Art Nouveau tiles sell for quite a lot of money nowadays - depending on the size and make, prices range from $45-$95 up to $400 each. In the inner west of Sydney, there are a wide variety of 100+ year old tiles adorning the front stairs of many houses.
Here are some for starters but don't go adding up the till yet - try removing them without breaking any... because of this, it's mostly the unused tiles that sell for a bucket load.
