Lead glass is only used for the back and sides of the tube. It can't be used for the faceplate because x-rays make it turn brown. Instead, barium-strontium glas

Lead glass is only used for the back and sides of the tube. It can't be used for the faceplate because x-rays make it turn brown. Instead, barium-strontium glass is used for the faceplate. It seems that use of lead is only a cost optimization, and the whole thing could use barium-strontium glass instead. Searching for "lead glass CRT browning" on Google found this sample chapter from an unidentified book, provided by the The Society of Photo-Optical Instrumentation Engineers, which includes some details: https://spie.org/samples/TT54.pdf https://spie.org/samples/TT54.pdf