I finally got around to making my new small, 2 brick gas forge. I used some Insulation Brick 23GD - 230 x 152 x 76mm, so a bit bigger than ordinary bricks. It's easier to do it in two halves, because you can carve the chamber out much more easily. I used a spoon,as the bricks are quite soft, and also used a rasp to finish. My blow torch is not a beast by any means but it does the job quite well. The fire cement has not cracked at all, so far anyway, but the bricks have developed a few cracks. I don't think they are much of a problem though.
Once carved, both halves of the chamber are lined with refractory cement, then attached together, simply by using garden wire. The joints between both bricks received some refractory cement too, that was a bit more difficult due to the relative narrowness of the chamber, but not too bad. Then I folded a sheet of aluminium around it to protect the soft bricks. Then I put the whole caboodle into the cooker's oven for a couple of hours to cure the cement.
I fired it today and forged a couple of blades out of some 3/8" Silver Steel . So far, I am very pleased with it: it gives out plenty of heat for small blades and I can use it inside my workshop, with the door open for ventilation of course! Until I can come up with a more imaginative maker's mark, I am going to stamp my initials JD on the blades.
I have put the whole thing on top of some more refractory bricks, to prevent any risk of scorching the bench. The outside of the forge does get warm but not too badly, so there shouldn't be any problems.