11 But now I have to seek the exact solution of this seeming discrepancy. For they who make light of the prophets, allege that the Prophet says on the one hand, And I cast them into the house of the Lord, into the foundry, but the Gospel on the other hand, And they gave them for the potter's field. Hear then how they are both true. For those conscientious Jews forsooth, the high-priests of that time, when they saw that Judas repented and said, I have sinned, in that I have betrayed innocent blood, reply, What is that to us, see thou to that. Is it then nothing to you, the crucifiers?
But shall he who received and restored the price of murder see to it, and shall you the murderers not see to it? Then they say among themselves, It is not lawful to cast them into the treasury, because it is the price of blood. Out of your own mouths is your condemnation; if the price is polluted, the deed is polluted also: but if you are fulfilling righteousness in crucifying Christ, why do you not receive the price of it? But the point of iniquity is this: how is there no disagreement, if the Gospel says, the potter's field, and the Prophet, the foundry?
Nay, but not only people who are goldsmiths, or brass-founders, have a foundry, but potters also have foundries for their clay. For they sift off the fine and rich and useful earth from the gravel, and separate from it the mass of the refuse matter, and temper the clay first with water, that they may work it with ease into the forms intended. Why then do you wonder that the Gospel says plainly the potter's field, whereas the Prophet spoke his prophecy like an enigma, since prophecy is in many places enigmatical?
Source: Catechetical Lectures (New Advent)