Penetrating Ink
Ink that contains a penetrating dye that goes into the fibers of the print-receiving material and shows through to the back of the document. It is usually used in passports and travel documents for applying numbers by letterpress printing.
![](https://static-content.regulaforensics.com/Hardware-products/knowledge_hub/glossary_documents/PENETRATING_INK/1l.webp)
a
![](https://static-content.regulaforensics.com/Hardware-products/knowledge_hub/glossary_documents/PENETRATING_INK/2l.webp)
b
![](https://static-content.regulaforensics.com/Hardware-products/knowledge_hub/glossary_documents/PENETRATING_INK/3l.webp)
c
![](https://static-content.regulaforensics.com/Hardware-products/knowledge_hub/glossary_documents/PENETRATING_INK/4l.webp)
d
![](https://static-content.regulaforensics.com/Hardware-products/knowledge_hub/glossary_documents/PENETRATING_INK/5l.webp)
e
Fig. 1. Hungary. Passport issued in 2002:
a — page spread (page 32 – data page). Paper substrate (page 32) and polymer substrate (data page); b — the same. Blank number. Front side. Penetrating ink; c — the same. Document number. Back side. Traces of red dye on the reverse side of the print. Oblique light; d, e — the same. Zoomed fragment. Front (d) and back (e) side of the print. Letterpress
![](https://static-content.regulaforensics.com/Hardware-products/knowledge_hub/glossary_documents/PENETRATING_INK/6l.webp)
a
![](https://static-content.regulaforensics.com/Hardware-products/knowledge_hub/glossary_documents/PENETRATING_INK/7l.webp)
b
![](https://static-content.regulaforensics.com/Hardware-products/knowledge_hub/glossary_documents/PENETRATING_INK/8l.webp)
c
Fig. 2. Slovenia. Travel document (Convention of 28 July 1951) issued in 2016:
a — page spread (front endpaper – page 1). Paper substrate; b, c — the same. Blank number (b). Zoomed fragment of the symbol (c). Penetrating ink. Letterpress