On the right side of the head, one of the two pieces is intact and the other split down the middle. The two parts were floating around inside the head.
One thing that is a little bit confusing is that Schott seems to make 4 grades of heat absorbing glass (KG1,2,3 and KG5). Looking at the transmission graphs, it seems the lower the number, the higher the transmission, but also the wider the transmission curve and the further it extends in the direction of near infrared.
And this graph from the Schott glass webpage:
The glass Edmund sells is 3mm thick. The glass in the Ilford head is 2mm, in fact mine measured 1.8mm. It fits in a channel in a metal frame. I havn't measured then channel but I suspect you really need the 2mm.
While we are on the topic, anyone know a source for the color filters? Mine are OK for now, so it's more curiosity.
I'm not sure how your glass fits in the holder but being broken in two pieces may not be that much of a functional problem. For example, the heat absorbing glass in the 500W Bolex projector is 4 individual rectangular pieces.
My piece is 15m x 30mm x 2mm. I might be able to put it back in somehow - it's a clean break. Not sure.
Mine on the other hand is truly broken, and one side missing completely.
Mine is also broken - I have two pieces about 15x15, plus another 15x30 piece still in the enlarger.