The colours of Charbonnel are ground 3 to 5 times; for a 100 liter ready made product, the grinding takes about 6 hours and five times about 12 hours..
CONDITIONS DURING THE GRINDING
While making the pigment paste it may not become too warm (friction) because the consistency of the oil may change making it too thick. Mixing must be done slowly and should be interrupted regularly.
After mixing the paste, it stays over normally a whole night, allowing the pigment to absorb the oil completely, before grinding starts.
During the grinding the space between the rollers is changed as the grinding progresses. The distance between the rollers is made smaller each grinding run, except during ther last run. During the last run the space must be slightly more, allowing the paste to be mixed thorougly.
QUALITY CONTROL
After grinding, three quality criteria apply:
COLOUR:
The colour will be compared with the standard colour as well as the transparency.
CONSISTENCY:
The consistency of the paste is checked; adhesion properties (tack), viscosity, and wiping properties.
The adhesion properties are checked by applying some ink on to a glass plate with a spatula. The ink should not stick to the spatula and form a layer on the glass surface.
Wiping properties are checked by applying ink to a plate and wiping it with tarlatan of paper.
SIZE OF THE PIGMENT PARTICLES
This is cheched with a gauge. Some of the ink is applied to the gauge with a scraper. Depending on the thickness of the ink layer in the gauge, the ink should be uniform, without visible particles.
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