Any script used over a long period of time undergoes changes, some of which may not be perceived by one unfamiliar with the development of the letter forms.
In order to date a script, one has to be familiar with its style—all the details characterizing a particular script at a certain time and place—while ignoring the personal features of different scribes or engravers. The paleographer deals with details of the letter forms, such as the changes in the individual strokes and in their meeting points with one another, their relative size, the stance of the individual letter, etc. An untrained eye will not be able to define all of these details and may easily be deceived by inaccurate comparative letter charts.
John Rogerson and Philip Davies themselves admit that the forms of certain letters in the Siloam Inscription do not resemble their later forms appearing in epigraphical material from the Hasmonean period. Yet they state, “The burden of proof is on defenders of the Iron II dating to prove the impossibility of a late Second Temple dating … It does not suffice to claim that the script can fit an Iron II sequence.”
Two Second Temple scripts present themselves for comparison—the paleo-Hebrew script on Hasmonean coins and the paleo-Hebrew script among the Dead Sea Scrolls. Both of these scripts lead us to conclude that the Siloam script fits best into an Iron II (First Temple period) sequence. The script of the Hasmonean coins is an artificial, archaized script that differs in details from the Iron II script. The script of the paleo-Hebrew scrolls from Qumran shows a late stage of a continuous, although slow, evolution of the early Hebrew script and likewise differs in details from the Iron II Hebrew script.
If the Siloam Inscription were inscribed in the Hasmonean period, its script would reveal a late stage of evolution (like the paleo-Hebrew scrolls) or artificial archaized characteristics (like the Hasmonean coins). It displays neither.
One who accepts a late dating of the Siloam Inscription must date to the same time all the Hebrew undated epigraphical material with script showing a similar stage of development. Such a late dating of the Siloam Inscription would also require us to move down the date of such clearly stratified material as the Hebrew ostraca from Arad and Lachish, ostraca that were dated by associated pottery as well as by paleography. It is impossible to move these down as the authors suggest.
Apart from paleography, there are additional aspects that must be taken into account when dating the inscription, such as its language and orthography and the material and techniques of its engraving, all of which point to an Iron II date and preclude a Hasmonean date.