Delft casting® technique
Errors with Delft casting technique: edge of cloisons not equally high
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| Example of a photopolymer mould. The edges are well formed and sharply delineated. Note that the edges of a cloison are not exactly vertical: there is a tendency towards rounding off. |
- Error in the mould. Ascertain that the edges of cloisons are well formed and equally high and thick in the mould.
- Poor impression of the mould in the clay. Press the mould down firmly, for example with a gluing clamp and allow the clay to settle while under pressure
- mould too thin, so that silver tends to solidify before completely filling up the mould.
- Lines used to delineate edges of the cloisons were too thin.
The above mould
looked quite acceptable. We have made one which is its negative:
the upstanding edges 
are now depressed, so that on casting a cloisonné
effect is obtained. A problematic feature of this mould, however,
is the combination of a thin silver plate and thin edges of the
cloisons. The mould will never be a perfect replica of the mould,
and the casting never be a perfect replica of the mould. The parts
which are likely to suffer proportionately the most are the thin
'lines', because the surface to volume ratio (and hence heat loss)
is the most unfavourable there. A typical feature of this problem
is that the crossings of two lines are well formed, but that in
other places the edges of a cloison tend to be depressed.
The same problem,
now more pronounced. The edges of the flowers were too thin in the
original drawing. The only remedy is to make them thicker and make
a new photopolymer mould to that end.
If the
lines in the original drawing are too thin another danger lurks, i.e.
that the edges of cloisons are so thin that one can hardly avoid washing
them partially out with water. The arrows point to portions where this
occurred. The problem is enhanced, of course, by prolonged washing and
by using a brush with hard bristles.
Errors: uneven thickness
If one side of the casting is thinner than the other, then it is likely that the two casting rings were at oblique angles. Do note that this is not entirely without risk. Not only may hot silver escape via the open fissure, but the air content of the mould will be larger: when air is heated to about 900 °C (1652 °F) by the silver the pressure increases fourfold and may throw off the top ring more or less explosively, or escape via the fissure, which may be the route of least resistance.
