Why Thailand still asks for a consulate stamp
An apostille is a single certificate that proves a signature or seal on a paper is real. It only works where both countries are bound by the treaty behind it. Thailand has joined that treaty, but it does not enter into force there until 28 February 2027. So today a paper for a Thai desk goes the long way: the Italian stamp first, then the consulate.
The 28 February 2027 change
Thailand's accession year is 2027, and the rule bites on 28 February 2027. Anything you need before then belongs to the old route, which is most files being sent this year. An apostille from Italy to Thailand becomes the whole story after that date. If your paper is for a use that begins later, it may be worth waiting for the shorter route.
From a Catania desk to a Thai one
Four hands touch the file. The issuing office in Catania prints a current copy. The Prefettura or the Procura legalises the signature on it, depending on who signed. The €16 tax stamp goes on each paper. Then Thailand's embassy or consulate in Italy adds the consular mark, and only after that does the bundle go east.
What you pay and how long you wait
The Italian cost is a €16 tax stamp per paper, with some kinds exempt. The consulate sets its own fee, so the Italian figure is never the whole bill. Timing is the real cost here. Sicily is a long way from the consular desk, and a bundle that misses a courier cut-off loses a day at each end. Send papers together rather than one at a time.
What the Thai side expects to see
A Thai desk reads the file in Thai, so a translation usually rides with the original and the stamps. Dates are read in the local calendar, so make sure the day and month are unambiguous in the translated text. The apostille requirements for Thailand will not change what that desk wants inside the envelope: a clean original, a faithful translation and names that match your passport.