Polarization modulation for solar vector polarimetry can be performed in various ways. Ferroelectric liquid crystals (FLC) have the advantage of allowing modulation frequencies of up to several kHz, therefore avoiding spurious signals due to seeing. A new modulation scheme using two FLC modulators was designed for the SOLIS Vector-Spectromagnetograph (VSM). Here we present experimental confirmation of this modulation scheme from a laboratory setup using a fast CCD camera running at 300 frames per second. Furthermore, we also show measurements from a circular polarization modulator that operates at 854 nm but uses one FLC built for 630 nm. This provides a means to cover a large wavelength range with a single, chromatic FLC modulator.