Can a blessed item be blessed again, and what does a blessing actually do?

This whole area of blessing is a little up in the air. If I had the opportunity I would ask Father Ripperger what a blessing is, what it does, what kind of power it has, how long it lasts, and whether there is precedent for this, because we treat it a little mysteriously as Catholics and nobody has ever really defined what is going on. I am all for holding an object blessed by a priest or bishop as sacred, like the chalice, but on mundane things, what does it mean to bless it, and is something emanating from that object? As I understood it, a blessing is like the cap put on the end of a liturgical prayer, like the priest's blessing at the end of Mass, applying to you everything that was done; the blessing is nothing in itself that adds to it. In the olden days, if you dipped your finger in the holy water font, you got, say, three hundred days off purgatory, because we believe a material object can actually hold the actual grace of God, which is transferred to you when you bless yourself. Whether the Church would still hold to that, I am not sure. This whole subject came up more sharply because the pope started saying it is okay to bless homosexual couples, so now we need to know what the power of a blessing is, if there is any, because it is an area that needs some work, and I do not think it has ever been done.