Reading through your replies to various comments it looks like glass or porcelain tiles are best to use and to use a thinset mortar to bond and grout the tiles.
Tiling a pizza oven dome.
Then using a string and marking pen build a compass half the diameter of your oven 18 or 21 and mark the circumference of your oven floor.
Given the variety of colors and styles of tiles available at hardware stores the design possibilities are huge.
It is to do with the sand and afterward place the bricks onto them.
These ceramic and glass tiles present a very convenient medium to finish the dome of the oven since their flexibility allows them to repeat the shape of the dome.
I love in the north east of england in the uk we have an outdoor pizza oven which i am looking to mosaic tile.
Construction of an igloo dome does not necessarily require a frame if completed by a competent brick layer.
To get a perfect shape dome put the sand in the shape of a dome.
A brick pizza oven dome is usually constructed as either an igloo or barrel dome out of medium density fire bricks both shapes are constructed in much the same fashion with bricks mortar and usually with a supporting frame.
You can also frame and decorate the front portion of the dome arch with granite or other materials.