The addition of carbon to samples, during transmission electron microscope imaging, presents a barrier to accurate analysis; the controlled deposition of hydrocarbons by a focused electron beam can be a useful technique for local nanometer-scale sculpting of material. Here we use hydrocarbon deposition to form nanopores from larger focused ion beam holes in silicon nitride membranes. Using this method, we close 100–200 nm diameter holes to diameters of 10 nm and below, with deposition rates of 0.6 nm/min. I-V characteristics of electrolytic flow through these nanopores agree quantitatively with a one dimensional model at all examined salt concentrations.