You don’t use soulfire to imbue an artefact with power, for example Harry could use soulfire to upgrade his duster, but doing so means his duster can be used against him if it fell into the wrong hands.
Better for a one time working such as the ice wall in BG when the spell dissipates so does the soulfire in it.
Harry is an artificer, so better to use soulfire to make something he could not otherwise make, but not use it to imbue it with power. He could use it to make a shield bracelet with the potential to be far more efficient and flexible than previous attempts by removing impurities and flaws from the metals, in a way not otherwise possible, for example, but only use his power in setting the spells on it. Imagine tiny shields of the purest gold, silver, copper etc with no impurities, no flaws, no tarnish, blank and ready to take a spell, because Harry cast them in molten form and used Soulfire to purify but not empower them.