ng to say.

Observe, then, that up to the point at which actual fusion
commences--that is, when pigment and glass begin to get soft--there is
no advantage in slowness, and therefore none in the use of fuel as
against gas--no possible _disadvantage_ as far as the work goes: only it
is time wasted. But where people go wrong is in not observing the vital
importance of proceeding gently when fusion _does_ commence. For in the
actual process of firing, when fusion is about to commence, it is indeed
all-important to proceed gently; otherwise the work will "fry," and, in
fact, it is in danger from a variety of causes. Make it, then, your
practice to aim at twenty to twenty-five minutes, instead of ten or
twelve, as the period during which the pigment is to be fired, and
regulate the amount of heat you apply by that standard. The longer
period of moderate heat means safety. The shorter period of great heat
means danger, and rather more than danger.

Fig. 42 is the closed gas-kiln, where the glass is placed in an enclosed
chamber; fig. 43 is the open gas-kiln, where the gas plays on the roof
of the chamber in which the glass lies; fig. 44 shows this latter. But
no written description or picture is really sufficient to make it safe
for you to use these gas-kilns. You would be sure to have some serious
accident, probably an explosion; and as it is absolutely necessary for
you to have instruction, either from the maker or the experienced user
of them, it is useless for me to tell lamely what they could show
thoroughly. I shall therefore leave this essentially technical part of
the subject, and, omitting these details, speak of the few _principles_
which regulate the firing of glass.

[Illustration: FIG. 42.]

[Illustration: FIG. 43.]

[Illustration: FIG. 44.]

And the first is to _fire it enough_. Whatever pigment you use, and with
whatever flux, none will be permanent if the work is under-fired; indeed
I believe that under-firing is far more the cause of stained-glass
perishing than the use of untrustworthy pigment or flux; although it
must always be borne in mind that the use of a soft pigment, which will
"fire beautifully" at a low heat, with a fine gloss on the surface, is
always to be avoided. The pigment is fused, no doubt; but is it united
to the glass? What one would like to have would be a pigment whose own
fusing-point was the same, or about the same, as that of the glass
itself, so that the surface, at least, of t