The Wednesday after Quinquagesima Sunday, which is the first day of the Lenten fast.

The name dies cinerum (day of ashes) which it bears in the Roman Missal is found in the earliest existing copies of the Gregorian Sacramentary and probably dates from at least the eighth century.

The ashes used in this ceremony are made by burning the remains of the palms blessed on the Palm Sunday of the previous year. In theblessing of the ashes four prayers are used, all of them ancient.  

yeah, BUT WHAT ARE THEY?