Why the paper exists
Before a foreign registrar holds your date, they want proof that you are free to marry. In Italy that proof is a single-status sheet, drawn up by the civil registry desk at your Comune. It states plainly that nothing on record bars the marriage. Couples who ask early keep the route calm, and knowing how to legalize a Certificate of No Impediment up front is half of that calm.
How fresh it must be
Age is the trap on this route. Registrars abroad want a sheet printed recently, and some are stricter than others. Ask yours for a date in writing before you order anything at all. Then work backwards: print the sheet, stamp it, land it with weeks to spare. Book the embassy attestation of a Certificate of No Impediment in Bologna only once the Italian stamp is already on the sheet.
The Italian stamp
A civil-status sheet is an administrative one, so the Prefettura in Bologna is the desk that stamps it. A prefecture is the arm of the state in the province, and this is the work it does. Court judgments and notary deeds go elsewhere, to the Procura della Repubblica, but yours does not. This first stamp is the Italian leg of consular legalization of a Certificate of No Impediment in Italy, and nothing travels without it.
Then the consulate
After the Italian stamp comes the consulate of the country where you will marry. That slot is the embassy legalization of a Certificate of No Impediment in Bologna, and slots thin out in wedding season. Take the stamped sheet, your passport and, where they ask, a spare copy for their own file. Whether the consular step applies at all rests on where you marry, so put the question to the registrar who will read it.
Cost and timing
The Italian side asks for a €16 tax stamp, the marca da bollo. On top of that the consulate charges a fee it sets itself, so ask for the figure of the day when you book. Plan on 10–15 business days for the pair of stamps. Where the date is tight, a rush route can close in 3–5 business days. Couples who want to legalize a Certificate of No Impediment in Bologna in one clean pass should still book that rush early.