Optically Variable Ink or OVI is a special kind of ink used as marker in important documents as an anti counterfeiting measure.Depending on the angle of view, the ink shows two colours generally, orange, blue, green etc.The OVI is highly useful to show the authenticity of the documents since the use of the ink is strictly controlled and not available easily.
Optically variable inks or OVI contain tiny flakes of special film which changes colour as the viewing angle is varied. OVI is a very expensive ink and generally used only in small areas of the document to mark emblems, identity marks etc.Silk screen printing method is sometime used to make OVI documents. It is widely used to make marks in currencies.
Depending on the angle of incidence of light, the OVI reflects different wavelengths of white light. As a result, a colour change feels when viewed with unaided eye. If the document is copied using a scanner, only one colour will apperar in the image so that it is easy to check the documents with the original one. OVI is considered as the most complicated type of ink to prevent forgery of documents.The ink has a colourful metal luster with two colours.Various combinations of colours are Red-Green, Gold-Silver, Green-Blue combinations.When viewed under sunlight, the ink gives two colours with optical variation and sharp colour change.Due to its complicated ink production procedure, huge investment, high anti-forgery reliability, it has become an excellent anti-forgery ink. More over, the ink is higly resistant to environmental factors such as sunlight, moisture etc.
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