Penetrating Ink is ink that contains a penetrating red dye that goes into the fibers of the paper and will show through to the back of the document.
Penetrating Inks are commonly used on the Arabic and MICR numbering of negotiable documents to deter forgers from trying to scrape the number off the document. If the number is scraped off, the red stain remains on the document.
This Penetrating Inks feature is effective primarily in document-present situations where the original document can be examined by a trained professional or scanned with a specialized 3-illumination ID scanner and analyzed with adequate forgery detection technology.
Usability is challenging as the examination is made not on the physical document but on a photograph or scanned image of it.