Watermark (from Latin filum, thread, and granum, grain) is a drawing which appears on some papers when viewed with a certain transparency. However, this term comes from the jewelry, not the paper industry.
In handcrafted, this effect is obtained during the fabrication of the sheet by a local reduction of the amount of fiber; There are two kinds of modus operandi. You should know that the watermark in the sheet is formed through the drain roller (for a flat table machine. So we work on the "fine linens, which are on the whole surface of the roll.
The watermark "line" is obtained when wires of copper are welded on the canvas. These wires make "clear" in the sheet, which is found by transparency in the paper. Commonly used for drawings without relief, or simple texts.
The second type of watermark, called "shadowed" is produced when this canvas has been "embossed". We engrave a punch into two parts, male and female, and the relief is applied to the canvas by "smashing" the fabric between the sides of the punch. This method is used when drawing the watermark is complex, when there is "black", or when the drawing has "multiple layers".
If the first watermark enabled papermakers to put a personal stamp on their production, this method is mostly used for sophisticated possibilities of ensuring the authenticity of official documents (paper money, stamps, identity cards, etc.). Since 2000, prescriptions written by doctors in France are secured by watermarks.
In 1862, the Bank of France produced the first "shadowed" watermark representing a human head. A century later, the watermarks are ever more refined to deter forgers who have significant technical resources.