Welcome to the Glass Message Board, Taco-- glad you decided to join.
Taco do you know where those 18 went!
Please everyone, keep an eye out for these half-bricks!Here's the same picture from the auction, just embedded. [Wonder what the rights status of this image are? I'd like to use it on my forthcoming Falconnier page]:

Half-bricks are much rarer than full bricks since they were only needed for the top and bottom courses. Find me one and I will exchange it for its own weight in Larks' Tongues, Hummingbird Wings, Butterfly Sneezes, Chicken Lips, Bottled Ghosts, whatever you want!
I had an idea about the brown brick which started this thread: the shape reminds me of pre-cast concrete blocks used to make retaining walls. They are meant to be arranged in curves, hence the angled sides. Using a brick with a [isosceles] trapezoidal section would be better for making a curved wall than the normal brick.
Which doesn't explain the
fairly unattractive brown color. The only 'colored' one I've seen so far ('colored' defined as not clear, not aqua) has been a very nice emerald green, something which would be agreeable in a wall (all green? just the occasional accent?). But a bottle-brown wall, hmm.
The seller wanted a couple hundred bucks for the brown thing, which I wasn't inclined to risk, what with having recently lost > $500 on what turn out to be an irradiated insulator. But it sure seems like a glass brick!
--ian