Q: How did the custom of signing ashes on the forehead for Ash Wednesday become dominant in English-speaking countries, while other places (like Rome) still typically sprinkle them on the head? Any sources you could point to would be helpful!
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A: I don’t know the answer to this, and I’m not even sure how to research it. This much I can tell you:
The previous English translations of the missal, the Sacramentary, said, “The priest then places ashes on those who come forward.” That is a good translation of what it said in Latin, and of what it still says in Latin. It makes no reference at all to the head or the forehead.
However, the English now says, “Then the priest places ashes on the head of all those present who come to him.” It put the words “on the head” into the translation where it isn’t there in Latin, in spite of the missal’s highly-touted literalism.
In the preconciliar rite, the only mention of the head is in reference to what the celebrant would do if there were no other worthy priest to impose ashes on him: He then placed ashes on his own head.
I gather that the other preconciliar rubrics for that day presume ashes go on the head, but they do not explicitly say so.
So no rubric that I can see ever explicitly called for ashes on the forehead. The rubric in force today says a little more in English than it does in Latin, which does not explicitly say where you put the ashes. That could explain variations in traditions.