The study of ancient hand-writings, the conventions and styled that they followed. Palaeography is important for the dating of ancient documents.
Here's an example of what palaeographers do (aleph in the quote below is, in this context, the first letter of the Hebrew alphabet):
The aleph has two parallel strokes, a form which started to appear at the end of the eighth century []. This practice is different from the earlier form of the aleph which consists of a v-formed pair of strokes crossing the vertical bar open to the right. This form dominates up to the middle of the eighth century, coexists with the two parallel strokes in the eighth and seventh century, and then regains dominance in the sixth century []. On plaque one the two parallel strokes in the aleph cross over the vertical bar []. Evidence for this is found in the last quarter of the eighth century and the first half of the seventh century.
]. This practice is different from the earlier form of the aleph which consists of a v-formed pair of strokes crossing the vertical bar open to the right. This form dominates up to the middle of the eighth century, coexists with the two parallel strokes in the eighth and seventh century, and then regains dominance in the sixth century [
]. On plaque one the two parallel strokes in the aleph cross over the vertical bar [
]. Evidence for this is found in the last quarter of the eighth century and the first half of the seventh century.