Metal Stems
(Blowing Glass in Metal)

Rev. ... 2002-12-15,, 2009-01-24, ... 2010-03-01 (divide forge & stems), 2012-03-08

 This page collects information for my site about blowing glass into metal forms, mostly my explorations, but some general info.
Most commercial metal and blown glass pieces have glass bulging through holes in the metal forms and in most cases the glass has been left unfinished until after annealing when the extra above the rim is sawn off square leaving a flat ground edge of some harshness. 
I wanted to work the glass after it was in the metal to form the lip, eventually to choose styles that would make it clear that it had to have been done that way. So I pursued casting metal bases to form stem cup and bowl forms (here and below) and the explored twisting up stems from steel wire.
In both cases, a theme was the setting sun behind dark bare tree branches to make a form that would look like the exposed roots, trunk and limbs of a tree and to blow glass into the shape formed by the limbs.

Related pages
Metal Center
History - Metal shapes to receive blown glass are nothing new, although older items known to me are just glass lined food and drink containers where the mold or hand blown glass fits into a metal form to safely hold the food.
Today metal lamp and vase forms with glass bulging through designed openings can be found in garden and decorative centers imported from Mexico and China.
Techniques and Tools  - If my goal is to work the lip of the glass in the goblet, then I have to be able to return the glass to the glory hole after taking it off the pipe, which means I have to have it mounted on a punty. (Glossary)  Among choices would be to leave a hole in the bottom of the metal form to attach to the glass, which affects the design choices for the piece. Another choice would be a large version of the prong gripper that is used in making light glass goblets and by lampworkers and I actually built a version and came up with a revised design, but realized as I cast some units that a different plan was needed - the gripper was not strong enough and depended on a disk type base.
Low resolution image of wire gobletThe wire goblet stems I fooled around with were unmanageable unless given good handle and the central wire provided the clue to a solution for the problem:  I could provide a small hole to take the wire, hold the leg with a retainer and release the hot metal and cooling glass into the annealer.  It would not be difficult to add a rod to a cast goblet.
Metal goblet base punty assembly Punty built for wire stem goblets - the outer end which has been braised in and drilled to only 3/16" (4.76 mm) to center the wire.on the foot plate/floor flange at left. There is an angled hole drilled in the side of the all thread (D on the other side) to permit running a wire down the inside to hold a leg of the punty, but both so far I have used light wire twisted through one of the holes in the plate to hold the wire stem, cutting it with diagonal cutters just before putting it in the annealer.
This unit makes use of common plumbing parts and not quite so common lamp parts.  The threaded portions size is what is called 1/4" IPS water or gas pipe, which is actually just over 1/2" OD.  Black iron pipe 4' long (A) takes a coupling (B) and a piece of fully threaded pipe used in lamp making (D) which has two lock nuts on it (C, E) and a floor flange (F) which is used to mount pipe as handrail or shower rod.  Black iron is used because galvanized gives off nasty fumes when heated.
Goblet casting after cleanup and threaded rod addedThis tool was rebuilt changing the long all-thread (D) to a much shorter piece which was filled with portion of a bolt that was center drilled and threaded 8-32. (result) to take a knob making mandrel.  This in turn was used for to mount a cast goblet with a threaded rod in the bottom.
  I got an email asking how I had time to install it on the punty while working and the answer is that I don't try - the metal shape in installed before I start.  The question is based on the glass working method where a bubble is used to pick up hot color or a color cup from a kiln.
  I mount the base to the punty cold, sliding or threading the rod into the hole in the punty and then securing the base from rotation.  I heat the unit in the gloryhole or in my hanging glass garage, and prop the punty at an angle with the open cup pointing at me from below waist level with the handle end of the punty on the ground.  I am not inserting the glass in the cup while the cup sits on the ground or something and then attempting to put the glass/base unit on the punty.
  If I had a situation where the only way I could get the glass into the cup was to come straight down, then I would mount the punty vertically and go up a ladder or stand to get above it - kind of like Stephen Rolfe Powell does here (scroll up and down.) 
  When I first tried blowing into the brass and the aluminum castings, putting the hot glass in the metal would chill the glass - stopping it from moving - and heat the metal - expanding it - leaving the glass loose in the metal and very awkward for working the lip, which was my goal. So I took the metal part, already mounted on the punty, and preheated it in the glory hole with one hand while maintaining the bubble/parison with the other. I could have used my special glass garage  for the same purpose. With the metal already warm (not forgetting that aluminum melts at about 1300F and brass/bronze at about 1800F) it was already expanded mostly and did not chill the glass as much so the glass could follow/flow to fill better.

Something has to be done to keep the base from rotating on the punty. I tried various techniques, including trying to screw it in very tight and running a wire up the shaft and out the side, but found that using soft steel wire around one of the feet of my stem wired through a hole in the flat end of the punty worked the best. Obviously, if the foot were round, it would be a problem. I suspect I would cast on a stub if it were round to keep it from rotating and to be cut off after blowing.

Design Factors - When blowing into metal for later working of the lip, and to a certain extent for later use, it may be necessary to avoid a perfectly round shape either by using an oval plan view or by providing indentions that provide a rotational grip on the glass.  I looked at some of the glass in metal works of Tiffany shown at the local museum and found features that suggested to me a choice of providing a piece that could be bent into the glass after annealing to pressure the glass, like the prongs on jewel settings in metal.  The brass/bronze metal I am using is very stiff and would resist bending.

As mentioned just above, if a design calls for a base that does not have a leg sticking out - a disk or a ball - it may be necessary to design into the casting a stub for wiring that is removed like the sprues but after blowing rather than before.

MF Goblet aluminum cast baseWhile some of my brass designs are heavy in weight, the aluminum ones are intentionally designed to be fairly thick to provide as much heat sink capability to reduce the melting that might occur on reheating.  Shown here are a tree form with sprues not yet removed and a tri-form after blowing the glass into it but before clean up of the metal surface.
Goblet cast of aluminum with sprues still attached.
Wire Rope Goblet Stems
The piece shown uses part of a piece of wire rope (about 15 feet long I found by the road and dragged home in a big loop on the bus!) that has 7 wires, a central straight wire and 6 twisted tightly around it. This is the natural tight pack. (By counting on a copper stranded wire, the next layer apparently has 12 wires in it.) Wire rope sample

I explored other packs for having choices in design and having a central wire for grip if I needed it.

Number of wires 3 4 5
Center wire dia. (fraction of D) 0.151 0.407 0.707
Center wire gauge for 9 gauge wire <24 17 12


WIRE STEM GOBLETS - Two images taken with different cheap video cameras (one a USB digital link, the other an X-10 analog remote-cast camera.) Low resolution image of wire goblet Low resolution image of wire goblet


An attempt at twisting up a piece out of (much too thin) 18 ga. stainless wire. It blew ok, but barely stands up. Thin stainless steel wire attempt at goblet

Second serious blown goblet (left photo outdoors on photo stand w/film, right 2 indoors with electronic PC-USB camera)
Good photo of second coblet, taken outdoors on photo stand Wire stem goblet Wire stem goblet

This is the third goblet blown into wire, a smaller gauge than above, using part of a batch of wire found being thrown out and bent up with a plate with 7 holes drilled into it

7 hole plate used for twisitng wires into cable/ropeProblems discovered while working the piece
- the hole in the punty was larger than the wire and it wobbled
- the wire is galvanized and the finish should have been removed after soldering or will have to be removed
- leaving the feet unset, at this angle, did not provide enough stability, although it could have been better tuned by trimming the ends.
Making the wire twisting plate.

Additional goblets have been made with cast feet and stems.

Wire stem goblet upside down




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