Page 2003-08-04 Rev. 2003-08-18, -19, 2004-06-27, 2007-01-02, 2010-10-23
Return to Sitemap
Three Piece Mold Blown glass (Three mold from
McKearin) is a classic way of producing glass,
requiring a mold in three pieces (amazing) that opens either sideways (2 sides hinging
off the middle section) or from the top like a blossom - which takes a special rig. I have
started building such a special rig, using 3 V-shaped steel forms to hold
aluminum (or wood) inserts. The V's are mounted on pivots with a ring
raised by foot pressure to open and close the mold. Besides the log mold,
I am making wooden masters to blow a three sided bottle with an insert to
"advertise" the people who buy the bottle. [And I got distracted in
making clay split molds for the same purpose.
I have an idea for blowing a votive candle holder that will look like a log and have recesses to hold votive candles so the light of the candles comes through the glass. The idea of logs with candles is copied from ceramic logs to be put in fireplaces with candles in them. The glass is, I think, unique. The sketch, right, made midway in the thinking, shows the basic idea. While drawing, remembering I was working blown glass, it occurred to me that a hole at one end, besides being necessary, would allow liquid into the bottle shape. And while writing this, it occurs to me that candle oil, colored or not, could be put in, without votive candles, but with wicks in the indentations. But I would still need those to bring the flame behind the texture. And with candle oil the liquid could not be above the flame! 2003-04-03
the right is a working drawing to scale of the end of the 3 piece mold to work
on the planning. Several smaller drawings were used during planning.
This drawing shows the 3 problems facing me. The inside of the mold
holding unit is 3" on each of the six sides, welded in pairs, so the three parts
open out. Each of the three sections poses unique problems to solve if
they are to come together.
the middle of the picture is the chunk of log, selected for size and a nice
looking tight bark. It was given 4-5 coats of shellac to seal the pores. Common
latex mold compound was painted on repeatedly, about 10 coats, drying to amber
between each coat. Finally medical gauze was laid on top and a couple of more
coats added. Before removing the latex from the log, a layer of plaster of Paris
was laid on, then another layer when the first was set, gauze was soaked in
plaster and added and more was painted on top. When all the plaster was "dry"
and no longer cool to the touch (about 3 days), the plaster and the latex were
worked off together, peeling the latex all around from the edges, the reinforced
plaster coming free early in the process.
Well, I tried making a plaster negative off the plaster positive and killed
the positive - too many undercuts and not nearly enough separator. So I
have cast another positive from the rubber mold and am going to do two things:
try to make a rubber positive from the rubber negative and form thin aluminum
foil on the plaster positive to omit undercuts in a detailed way. 2003-04-25
Finally thought my way through and got a good wax positive,
which I can use for a sand casting or a lost wax. To get a rubber negative
with less detail to get caught in plaster or wax, I took a stiff brush and
worked Crisco white fat down into the log's grooves, filling in the bottom.
I then took a cloth and wiped across the surface, removing fat in the details
nearer the surface. I then built up yet another latex mold backed with
gauze. This one came off reasonably good looking. Also, since I know
more about what I find interesting, I positioned it to pickup two branch lumps a
bit further over than I had before. Today, I melted molding wax and let it
cool down well below 190F so that it would be less liquid and less damaging to
the latex and poured several layers, shaping the outline as I went, to get a wax
positive. Now I will have to shape the rest. 2003-08-03
a year and a half, I have gotten back, somewhat, to the 3 piece mold assembly,
at least to take pictures.
I have looked at bottles for some time and wondered about
blowing the more interesting shapes, while also working on
neck molds for any shape I might make. So I
bent up some thin metal trays from aluminum flashing, too thin for much else,
and taped the joints with metal repair tape, greased the bottles, and melted the
wax. To keep the bottom of the mold reasonably thick, I took 1/8" wax strips,
stacked them and balanced the bottles on them. The necks were roughly
stuffed with clay to the shape of the mold. A step I missed was to make
sure the seam from the original molding of the bottle was level to be a guild
line for pouring the wax. So I added more wax, after adjusting the bottle
position and box.
As I have worked with trying to sand cast, I have been gradually pounding the sand more, being more careful about vent holes and spruing and being sure I have enough metal. I also added a lot more oil to the sand Although I have not used it yet, I made a plaster mold of the bigger bottle in a different aluminum shell with distinctly sloping sides. 2004-06-27
Contact Mike Firth