rounding over the sharp edge of a cut neon tube

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    wondering if i could ask a question, worried it's been asked many times
before, apologies if it has.
    i got a few 4 foot long broken lengths of neon tube.  i want to cut them
into approximately 16 inch long pieces and heat the cut ends to round over
and smooth off the sharp broken edges.  i was told i could use a
("bernzomatic") propane torch to heat the glass enough so it melts (and
rounds over the sharp edge).  i tried it and much to my surprise it worked.
i tried it on a few more pieces and i got erratic results.  on some it
worked fine, on others it caused a crack to run down the length of the tube,
about 3 or 4 inches.  this is what i don't want to happen.  can anyone give
me tips or pointers on how to heat the end to round off the sharp edge
without causing the tubes to crack?  i am so much hoping i'm not going to
need an annealing oven (cause i don't have one!).


Re: rounding over the sharp edge of a cut neon tube
On Wed, 3 Feb 2010 01:46:51 -0600, "William Wixon"

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Welcome to the wonderful world of glass! The best you can hope for is
to lightly play the flame over a good bit of the length (4 - 6"?) to
prevent just the end from getting hot, causing the sharp transition
from hot to cold, and the resulting thermal shock. If you have an OA
rig (and since you post to rcm, there's a chance you do), try using it
(careful - it's a lot hotter!) gently, and "insulate" the warmed areas
by turning down the O2, to coat the glass with soot (after you warm
it); this will help the glass to cool more slowly & evenly. Don't get
soot on the end when it's molten, though, or it might get embedded
into the lip.

Generally, the thicker the glass, the more problems you will see with
trying to do this sort of operation. The soot coating is a great way
to anneal thin pieces - regardless of their overall size. For somewhat
more mass, dropping the finished piece into a container of vermiculite
will do much the same. Above that, you need an annealing oven.

What are you gonna do with the tubing? Is it real neon tubing (clear
glass) or does it have the phosphor coating? Just curious.


Re: rounding over the sharp edge of a cut neon tube

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One thing people overlook is the simplicity of just doing things by
hand: a simple piece of fine sandpaper rubbed at ninety-degrees to the
cut will quickly remove any hazard, and it can also be used inside the
lip, should that be a concern. Any grinding routine will result in
dust, so the inside of the tube should be blocked if dust is going to
be a problem. Also, to avoid dust inside the tubes, store them
horizontally or put plugs in each end.

If you use a torch, one problem which might occur is that the glass
might become "reduced", causing it to turn black. This is caused by the
lead in the glass (neon tubing is technically "crystal", as used for
glassware, and crystal is more than a quarter lead). This can be
avoided by using more oxygen (if using an oxy-acetylene or oxy-propane
- the latter being used by lampworkers), but the only way to avoid this
using a Bernzomatic torch is to avoid playing any part of the flame
over the glass which contains unburned propane, as the propane will
"steal" the oxygen it needs to burn from the glass, reducing the lead
oxide in it down to plain lead, which is black in glass. Just use the
edges of the flame, and keep the flame moving so that no one spot gets
too hot - the hotter the glass, the easier it is for the chemistry of
the flame to react with it - if you just try to warm the glass and
don't rush it, you should get good results.

As for annealing: use very diffuse heat to warm the glass near the area
to be worked before you start to apply melting heat to the lip. After
the glass has rounded, apply more diffuse heat to the glass near that
area and a little down the tube, causing the heat to form a gradient
and avoiding having too great of a difference between any adjacent
areas of the tube (keep rotating it - always!). Gradually withdraw the
heat and you should reach a state of balanced stress which will not
break the tubing. All of this problem is caused by the fact that most
materials expand when heated: add that to the fact that glass is
brittle, and you can see how expansion can caused problems Using a can
of hot vermiculite for control of the cooling is nice, in theory, but
it really doesn't help for something as thin as neon sign tubing: it is
already too cold to be affected by the warm vermiculite - that cooling
technique is often used by bead-makers just getting started and unaware
of how to make their own annealing oven on the cheap, but this only
helps if the piece is thick enough to hold enough heat between torch
and bucket (or pan - an electric frying pan is sometimes used to keep
the vermiculite hot) so that the piece can self-anneal.

Unless you have a lot of this tubing, or unless you have a specific
project in mind, you might find it less costly to just buy the tubing
from a neon supply house - they might charge you to cut the glass, and
they might not be able to fire-polish the ends, so a trip to a
glassblower (a neon shop) might be in order: sometimes, if the worker
is interested in what you are doing, you might catch a break on the
price (some glassblowers are willing to give a break to those doing odd
non-profit projects while making their bread-and-butter off of those
with commercial interests - but most are poorly-dressed tightwads
uninterested in anything but the bottom line and who would take offense
that you would even consider taking up a torch on your own, so it might
be best not to mention your own trials unless you are copacetic or know
his or her temperament: there are glassblowers who have a reputation
for verbally bringing grown men to tears, just for the sport or because
of a (possibly permanent) bad mood (one name stands above the rest:
Gunther Weiss, founder of Weiss Scientific Glassblowing and once,
arguably, the best glassblower in the US - probably dead by now, but he
could make a complete stranger feel like trash). Hopefully, if you
complete your project and don't do any more glassblowing, you will be
safe from whatever causes glassblowers to be this way.


I am checking this group to see if it has enough action to be worth
supporting: I've been informed that my body will soon cease to support
life, but nobody knows why or how long it will take before I'm off to
the happy hunting grounds, so, while I'm physically going downhill and
unable to work, I thought I would start some glassblowing educational
work on the web, collecting the resources of various companies which
support glass research (such as the Bullseye Glass Company, started, in
part, by my friend Boyce Lundstrum), the American Scientific
Glassblower's Society (ASGS) and Corning and so forth - a lot of time
will be spent digitizing old publications and converting VHS films some
of which were converted from 16mm original films from the early 20th
century, but I'm sure that I'll get some help - those glassblowers who
are of the kind and charitable sort have been on the increase since the
early 90's, which was a time when I was working with ASGS to promote
information exchange (as opposed to the standing of the general
glassblowing community of that time that competition was to be
discouraged: a mall glassblower (lampworker) making dust-catchers would
turn off his torch should one of his observers mention that he was
interested in learning the craft - and I say "he" instead of "he/she"
because glassblowers are notoriously lonely and most of them are men,
so he might not turn off his torch to spite a woman the way he would a

If you know of a better place for the exchange of glassblowing
information, please feel free to mention it to me in EMail - zorondoug
at yahoo. On an aside: I used to be able to use just "zoron" as my
screen name, but Gary Larson came out with a Farside comic panel
showing a UFO crashed onto the Statue of Liberty with two aliens in it,
one saying to the other, "Is that a good enough look for you, Zoron". I
don't know if this is the only reason, though, as I discovered that one
of the sites I wanted to use with "zoron" was taken by someone in
Australia, and I don't know if they published Farside there. My "zoron"
appelation was created by my parents about the same time I was born, as
a name for their home-entertainment sales-and-service business, derived
from their names, Zoda and Ronald. Sorry, this new medication causes me
to be a bit wordy (as if I needed any help). If anyone knows anything
more of this name's use in the world, feel free to mention it.

Keep it hot!

R. Douglas Wiggins Jr.
"Zoron" - The Original (circa 1954)

We've slightly trimmed the long signature. Click to see the full one.
Re: rounding over the sharp edge of a cut neon tube
Hi, there is another trick you can use - get one of those single
electric burners - really cheap at walmarts - or try out the local
thrift store - you can also use a cheap crock pot for this.  Fill a
can vermiculite (for a crock pot skip this step, and just fill the
pot).  Turn your heating on to warm and place the tip of the rod into
the vermiculite, let this sit for about 30 minutes then turn up to
hot, let sit for another 30 minutes - take the rod out of the warmer
(use a heat glove if the other end is hot) and then slowly introduce
the tip into the flame, this will greatly increase your odds on not
cracking.  Place the heated end back into the warm vermiculite and let
the rod slowly cool (this really doesn't anneal as well as a kiln, but
it is better then nothing).   Your other option is to just score the
glass and do a clean break, then take a dremel tool with a glass
polishing disk (they have them at the hardware store) and polish your

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