Doctor's blade flaws in photogravure
Publicado: 28 Dic 2010 06:53
In photogravure, the little holes of which the design of a stamp is made of were meant to keep the ink, an area in the design without a "screen" of holes would lose the ink immediately while the cylinder turned. This screen is absolutely necessary but can be replaced by a set of diagonal lines that can hold the ink long enough till the ink sets on the paper and delivers the required design!
Bu the cylinder would also keep the ink stuck outside the holes for awhile, long enough to reach the paper and in that case the design would get blurred and smudgy! To avoid that a special, long and lean knife scrapes the superfluous ink off the cylinder without being able to get the ink out off the holes! This was called the "doctor's blade" in English or "Rakel" in German"or "racleta" in Spanish. The German word for photogravure is Rakeltiefdruck...
If the mechanism of the doctor's blade gets defective, the ink will be present - in a haze often - on the stamp. If the blade itself gets defective, with little indents in it, the indents of the blade will result in longish coloured lines, more or less following the direction of printing, the turning of the cylinders.
to be continued ...
Bu the cylinder would also keep the ink stuck outside the holes for awhile, long enough to reach the paper and in that case the design would get blurred and smudgy! To avoid that a special, long and lean knife scrapes the superfluous ink off the cylinder without being able to get the ink out off the holes! This was called the "doctor's blade" in English or "Rakel" in German"or "racleta" in Spanish. The German word for photogravure is Rakeltiefdruck...
If the mechanism of the doctor's blade gets defective, the ink will be present - in a haze often - on the stamp. If the blade itself gets defective, with little indents in it, the indents of the blade will result in longish coloured lines, more or less following the direction of printing, the turning of the cylinders.
to be continued ...