Products security elements
1. Watermark – the built-in security feature which can viewed in transparent light. There two types of watermarks:
1.1 registered – when the image is in one area of the paper. As a rule paper remains unprinted in this area.
1.2 Striped – when the same image is repeated one above the other or next to it, dark and light areas of the watermark alternate.
2. Security thread – a thin stripe made of polymer embedded in the paper and can be viewed in transparent light. This can be of two types:
2.1 Solid thread fully embedded within the paper, it can be visible on the paper surface, and it can be invisible to the naked eye but can be viewed if held against the light.
2.2 Windowed thread is embedded in the paper but some if its areas are visible on the paper surface and to the naked eye it looks like a broken line with paper bridges.
3. Microtext – either an image or set of symbols or text which can be viewed only at high magnification using a magnifying glass. Microtext can be positive when there are dark letters against light background, or negative when light letters or symbols are against a dark background. Type setting can be from 0.12 to 0.25 mm.
4. See-through feature - made up of images or their parts printed on the back and front sides which make up a complete picture when viewed in transparent light. Often the colour of such an image is determined by the image printed on the reverse side of the banknote.
Colour shift images
5. Colour shift images are security features which change their colour or become visible if viewed at different angles, e.g.:
5.1 OVI is optically variable ink which changes its colour from purple to yellowish-green depending on the angle of view.
5.2 Iridescence is often printed as a stripe or as a registered image and changes colour if the note is tilted.
5.3 Metallic inks have special metallic lustre
6. Latent image- an image which can be seen if the note is held at the eye level in reflected light.
7. Clear window – a hole in the paper which is covered with a clear polymer film and a printed image, embossing or other optical properties. The film itself is embedded in the paper.
7.1 Varifeye – a film with special optical properties adhered to the paper surface over a hole in the paper.
8. Blind embossing – an unlinked relief image printed on the paper, it is raised over the paper surface and tactile enough to feel.
9. Gold blocking - when the image is hot stamped on to the paper by metallic or holographic foil.
10. UV feature - an invisible image seen under UV light which can fluoresce in different colours.
11. Intaglio (or DP or metallographic) printing - the method of printing whereby images are raised over the paper surface due to a thick layer of ink which can easily be felt. Intaglio printing enables the printing of images of high accuracy and sharpness.
Lines of different thickness and direction
12. Lines of different thickness and direction - a set of lines of various thickness which interconnect at different angles. Where their thickness is changed it is possible to view letters or figures.
13. Rainbow printing - a subtle change of one colour to another by mixing the two. There is no clear line between the two colours.
14. Anti-copying feature - one of many security features to protect against counterfeits made with the use of black and white or colour photocopying machines. Security methods can be linear or raster.
15. Guilloche vignettes - continuous interlocking fine lines which form complex geometrical patterns (for borders, corners, overall mesh, rosettes, etc.). It is hard to replicate the guilloche on copying equipment as the thickness of lines is very small (from 0.04 to 0.07 mm) and due to the change in line direction. If guilloche is printed in intaglio then it is impossible to reproduce it.