GLASS ENGINEERING FOR CATHODE RAY TUBE MANUFACTURE (iv)

The luminescent screen of a CRT is composed of a mixture of barium and zinc salts in colloidal form which are applied to the internal surface of the face plate.  This was done by placing the tube face down on a work table and then adding a buffer layer of distilled water to an approx depth of two inches.   The luminescent mixture charge was suspended in a potassium silicate solution and quickly added to through the tube neck thouch a special funnel which had a shaped rose fitted to ensure minimal disturbance of the buffer layer yet ensured even distribution of the luminescent mixture.

The tube was then allowed to stand for several hours by which time the luminescent charge settled on the faceplate in an even deposit whilst the silicate formed a layer of gelatinous deposit on top which aided the stability of the settled film.    At the end of this period, the tubes were carried to a decanting table and secured to suction pads.  The table was slowly tilted until the supernatant liquor very slowly poured away leaving the luminescent screen deposit on the faceplate inner surface.  

When all supernate had drained, the bulbs were suspended on a hanging carousel and transferred to a drying table where a sparge tube was introduced through the neck to bleed cool filtered air into the bulb to dry any remaining liquid - just as shown in the photo below: -