It seems like a lot of the newbee's to engraving horn like to buy stock in Exacto knives and blades! The old sailor's who originated scrimshawing, commonly used a knife tip or sail cloth needles. Horn is alot softer than ivory, so is easy to engrave. Ivory on the other hand is harder. It doesn't seem to matter what a person likes to use, as long as the tip is kept sharp and you cut deep enough so the scratching comes out darker and very visible, when inked. Remember ware! Over time shallow engraving (scrimshaw) will ware or sometime disappear from rubbing and hard use!
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Rick