Jeremiah 17:1

The sin of Judah - Idolatry.

Is written with a pen of iron - It is deeply and indelibly written in their heart, and shall be as indelibly written in their punishment. Writing with the point of a diamond must refer to glass, or some vitrified substance, as it is distinguished here from engraving with a steel burine, or graver. Their altars show what the deities are which they worship. There may be reference here to the different methods of recording events in those days: -

1.A pen or stile of iron, for engraving on lead or wood.

2.A point of a diamond, for writing on vitreous substances.

3.Writing on tables of brass or copper.

4.Writing on the horns of the altars the names of the deities worshipped there. This is probable.

In several parts of India, and all through Ceylon, an iron or steel pen is used universally; with these the natives form the letters by incisions on the outer rind of the palm leaf. Books written in this way are very durable. This pen is broad at the top, has a very fine sharp point, and is sharp at one side as a knife, to shave and prepare the palm leaf. A pen of this description now lies before me.