It is widely recognised that the usual results of kiln forming are
one textured side and a smooth upper side. The common methods of having upper
and lower surfaces both smooth is to blow the glass, avoid allowing the glass
to touch the mould, and cold working the textured side to smooth.
The question arises about the possibility of getting
smooth surfaces on the inside and outside of a drop vessel. As the glass in a drop only touches the mould
at the collar and edge, shouldn’t the glass be smooth on both sides? The answer to that is in the temperatures and time used.
The temperatures used in a drop are not high enough to be
certain of smoothing the outer surface. But
the soak times at drop temperatures are enough to create a fire polish on the
upper/inside surface. This indicates the
blank in a drop should be placed with the texture up, facing the heating
elements. The smoother side facing the floor will be stretched and
will remain smooth.
The smoothing effect of firing with rough side up does
depend a little on the depth of the drop.
Shallow drops will not have the same heat exposure that deeper drops do,
assuming that a moderate heat is being used over three to four hours.
This implies that the design to show on the inside of the drop should be in contact with the separator when fusing the blank.
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