Last time we left this story we had a complete cathode ray tube bulb but we still have a few steps to go before we have the finished tube, so, what's next? Well, before the phosphor can be added to produce a luminescent screen, the interior of the bulb must be perfectly clean and this was done by pouring a portion of dilute Hydrofluoric Acid (HF) into each tube whilst situated on a shaking table where the bulb contents were continuously swirled for 20 minutes. HF is a particularly nasty commodity and is commonly used to etch glass and you may remember sachets of this reagent being sold along with a stencil set to allow you to permanently etch your car windows with your registration number - quite in vogue during the early 90's but I suppose 'Elf & Safety' and lefty nanny-ness has scuppered that particular usage these days!!!
After twenty minutes, the acid is tipped out, the bulb rinsed with tapwater and then given a final rinse with distilled water. Once washing was completed, the bulbs were supported on an suspended carrier system and passed through to the next production department and next process where the luminescent screen was laid down.
We'll take a look at the phosphor and luminescence laying process in a future blog entry.