The short period ( 0.94 -day ) transiting exoplanet WASP-19b is an exceptional target for transmission spectroscopy studies , due to its relatively large atmospheric scale-height ( \sim 500 km ) and equilibrium temperature ( \sim 2100 K ) . Here we report on six precise spectroscopic Magellan/IMACS observations , five of which target the full optical window from 0.45 - 0.9 \mu m and one targeting the 0.4 - 0.55 \mu m blue-optical range . Five of these datasets are consistent with a transmission spectrum without any significant spectral features , while one shows a significant slope as a function of wavelength , which we interpret as arising from photospheric heterogeneities in the star . Coupled with HST/WFC3 infrared observations , our optical/near-infrared measurements point to the presence of high altitude clouds in WASP-19b ’ s atmosphere in agreement with previous studies . Using a semi-analytical retrieval approach , considering both planetary and stellar spectral features , we find a water abundance consistent with solar for WASP-19b and strong evidence for sub-solar abundances for optical absorbers such as TiO and Na ; no strong optical slope is detected , which suggests that if hazes are present , they are much weaker than previously suggested . In addition , two spot-crossing events are observed in our datasets and analyzed , including one of the first unambiguously detected bright spot-crossing events on an exoplanet host star .