The reaction chamber in the arc production of fullerenes was redesigned with a nozzle surrounding the decomposition zone to allow for clean collection of soot in a filtering cartridge. Quantitative analysis in the region of 300–430 nm in UV-visible spectra permits determination of the abundance of C60 and C70 in the soot. Calibrated curves of absorptivity for both pure fullerenes were employed. In equivalent conditions of current and pressure, electrographites of different origins have different decomposition rates and yields. A mechanism to interpret the cathodic deposit formation is proposed. Decomposition inside a closed cathodic cylinder yields 100% deposit.