Monitoring the manufacturing process of a silica precipitation reaction is essential to better understand and take actions on the process, so that the final product meets the required specifications. Indeed, silica is a product with a wide range of applications (automotive industry, healthcare products,...) and according to the use, the specifications can be different. Visible and near infrared spectroscopy (VNIRS) is relevant to provide physicochemical information about the analyzed product. Moreover, this technology is suitable for in line or at line measurements as acquisitions are fast and can be performed with little or no sample preparation. In the case of complex samples, such as silica products, which both absorb and scatter light, it is necessary to implement better spectral measurements to improve the extracted information quality and therefore to optimize the process monitoring. The aim of this study is to test and compare the performances of 4 different optical set-ups providing different spectral measurements during the silica precipitation: (i)a double-beam laboratory spectrometer, (ii)a custom double integrating spheres (DIS)system, (iii)an optical setup based on Light Polarization Spectroscopy and finally, (iv)a Spatially Resolved Spectroscopy probe placed on-line. All these techniques provided us with multiple spectral information, which allowed us to solve optical transfer models and thus to access scattering and absorption coefficients. Results show that for every complex mixtures, there are specific light –matter interactions. From this study the best way to acquire a silica slurry spectrum was determined so as to extract physicochemical characteristics and to fully monitor the process.