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From: (Don Wilkins)
Newsgroups: rec.crafts.metalworking
Subject: Re: Glass working
Date: Wed, 06 Jan 1999 16:55:44 GMT

On 5 Jan 1999 15:13:33 GMT, "Don Foreman"
<> wrote:

>How do you keep from getting bubbles in glass when you heat it with a torch
>to fuse it?

Pyrex is not difficult. You must be using too much heat. I presume you
are trying to seal the end. Start with the tubing too far out and then
bring it in (while rotating) until you see the edges start to round
over. This stage is called fire polishing. You should do this to both
ends and when you do the second end once the edges start to round over
bring the tube deeper into the flame and you will see the hole get
smaller and smaller. Keep heating and turning until you see the last
of the capillary close. Try to keep the heat close to the end to avoid
getting a thick end seal.

Sometimes it helps to puff a little on the open end after it is
sealed. If you do this don't forget that you had that other end in the
flame. If you forget you wouldn't be the first one to get hot lips
blowing glass.

If you are using oxy-acetylene it is very easy to get too much heat.

>(Metalworking content:  I'm making thermocouple sheaths out of pyrex tubing
>for plating solutions)

I presume that you are making these for control rather than for
temperature measurement.

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