Given a flat injective ring epimorphism u from commutative rings R and U, we
consider the Gabriel topology G associated to u and the class D of G-divisible
R-modules. We prove that D is an enveloping class if and only if it is the
tilting class corresponding to a 1-tilting R-module and for every ideal J in G
the quotient rings R/J are perfect rings. Equivalently, the discrete quotient
rings of the topological ring End(U/R) are perfect rings. Moreover, we show
that every enveloping 1-tilting class over a commutative ring arises from a
flat injective ring epimorphism.