Here's a Mission tile frame with a 6" square Porteous tile.   The sides are 1.5" and the top and bottom rails are slightly recessed and 2.5" thick.  Corners are joined using genuine mortise and tenon joinery and then secured using two square through pegs on each corner.

The tile is a Porteous tile of Wellington, New Zealand in a high gloss.  It measures approximately 6"x6".  Truly a beautiful piece of work.

Frame shown is finished in a Stickley #32 (Onondaga) and is the frame and tile you'll actually receive.