I assume that he wants the CRT to look "normal" after it is let up to air... knocking/twisting/torching off the tip seal may allow enough inrush of air to blow off some of the phosphor. In cases like this, I wrap the tube in a heavy blanket, leaving the HV button exposed, and pound a sharp scribe point through the HV button. The tapered scribe can be pulled out slowly to control the inrush of air. I have done this many times and never had a problem. (don't miss and hit the tube
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jr