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Once insulators are
formed, they are dried
and glazed. The glaze
is made from clay that
is liquefied. When the
glaze is fired at a high
temperature it fuses
with the insulator and
produces a glass-like
finish. The glaze also
strengthens the insula-
tor and can be used to
fuse multi-part insu-
lators together. Lapp
insulator traditionally
used an orange-brown
glaze on many of its
early insulators, but
also used a chocolate
brown color. The 1928
catalogue mentions blue, light blue,
white or chocolate. Early insulators
were incused with the Lapp logo.
In 1927, Lapp began using an un-
derglaze with a date and catalogue
number. Large insulators were usu-
ally marked, but many small pin in-
sulators are unmarked.
When glaze is applied to an insula-
tor it resembles a flat paint.The shiny
glass surface appears only after the
piece is fired in a kiln at a very high
temperature. Initially, when the Lapp
factory was built on Gilbert Street,
there were two bottle kilns, then
four and by 1924, eight, all fired with
soft coal. They were 28 foot in diam-
eter and 35 feet tall. (The bottle kilns
were torn down by 1928.)
The “green” insulators were
stacked into the kiln and the kiln was
fired slowly until the temperature
reached 2,200 degrees. The temper-
ature had to be held for a long time
and then gradually cooled for several
days. A single firing could take eight
days. Robert Saulbury, remembering
those days, remarked “we weren’t in
such a hurry in those days. The boys
could do a little fishing if everything
was going well.” It was difficult to
maintain the proper temperature.
Any mistakes and the firing was a
loss. Men described intolerably hot
conditions when they had to pull the
still hot insulators out of the kilns,
not to mention the three “firemen”
who had to continually shovel coal
into the furnaces, twenty four hours
a day during a firing. Bottle kilns are
often called “periodic” kilns because
they were fired periodically.
In the 1920s, the tunnel kiln was
introduced, which allowed continu-
ous firing. A cart filled with green
insulators enters at one end and
travels the entire length of the tun-
nel, emerging at the other end com-
plete. The kiln is continuously heat-
ed so there is no down time. Lapp
had a tunnel kiln in 1925.
In the early years of electrical trans-
mission, there was a lot of trial and er-
ror, not only in the production of the
insulators, but also in the design and
engineering of the insulators them-
selves. Many of Fred Locke’s first insu-
lators that were sent to California for
an early electrical transmission line in
the 1890s were rejected. By the time
Lapp Insulator Company entered the
business in 1917, there was a lot more
science and technology that could be
applied to design and production.
In Lapp’s first catalogue, published
in 1918, Lapp makes reference to the
problems “Our organization is backed
by men of some eighteen years active
experience exclusively in this field
and recognizes the very active devel-
opment of the last six or eight years,
the trials and failures of that period
and we present our products and are
planning ahead in full knowledge of
this evolution and of the lessons it
teaches.“ This statement expresses
the concerns of an emerging industry
that was propelled into the modern
age by the need for reliable insulators
for the transmission of high voltage
There were many companies at-
tempting to design and manufacture
insulators. The competition was keen
and aggressive. Lapp prided itself on
testing and quality control. The Lapp
name became synonymous with in-
novation. Jack Tod in his book on col-
lecting porcelain insulators wrote:
“All the larger insulator companies of
Lapp Plant in 1924 with 8 bottled kilns in the background.The bottled kilns were torn down in 1928.
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