Hard enamel is never finished in a single firing. One of the least visible facts about a David Oscarson pen is how many times it has been through the kiln, and how much skill each of those visits demands.
From paste to glass
Each colour begins as a composition of glass, water and metal oxides, ground for hours by hand with a mortar and pestle until it settles into a fine paste. A quill is used to lay the paste over the guilloché engraving, and the component goes into a kiln at more than 1,000 °F. In the heat the paste fuses to the sterling silver and becomes a thin layer of glass.
Multiple firings
A single layer is too thin to fill the engraving. Each colour of hot enamel requires multiple firings, and each colour has its own firing temperature. After each firing the component is cooled, filed with a diamond file, re-enamelled, re-fired and filed again, until the enamel reaches the depth needed to cover the peaks and fill every valley of the guilloché.
Because many collection pieces feature several colours, many are fired fifteen to twenty times. Only after the final firing are they polished and buffed to reveal the velvet finish of the enamel.
Fire, file, re-enamel, fire again.
Patience and skill
Each pass through the kiln is a test of patience, experience and skill. The enameller has to judge temperature and timing for every colour, and every additional firing is another chance for something to go wrong. That is why the house requires a five-year apprenticeship before an enameller's work meets its standard.
Why colours are usually separated
Different colours require different temperatures. If two colours touched, the firing that suits one could spoil the other. For that reason, two colours of hot enamel are normally separated by an outlined border of silver, a fine wall that keeps each colour in its own field. Those silver borders are part of the familiar look of enamel work.
The exceptions
Some David Oscarson collections set out to do what the process usually forbids. Consider the Lilies was the first collection to place three colours of hard enamel onto one surface without dividing walls. The Carl Milles collection merges two colours without a border, over a meandering double-lined diamond-cut guilloché current that evokes the meeting of the Mississippi and Missouri rivers. The Alfred Nobel barrel merges four colours outward from white to yellow to orange to red to depict the blast of dynamite.
Each of those effects demands extra control at the kiln, and each is a reason those collections are admired by collectors who know the process.
What it means for the owner
The result of all those firings is a finish that does not fade, peel or wear like paint. Hard enamel is glass, so it resists scratching and keeps its colour for generations. Like any glass it can chip if dropped, so keep the pen capped and cased when travelling. Look closely at a finished piece under a single light and you can see the depth that fifteen or twenty firings build.