In phase contrast mode, gelation and deposition appear as darker regions in the raw microscopy images, allowing us to use intensity measurements as a proxy for the occurrence of gelation and deposition. To correlate video footage with ∆P (t), we first subtract the clean channel background from each frame. The numerical value of each pixel is summed to determine an overall brightness (I). Due to the background subtraction, bright regions correspond to gel deposits. We measure I in the first 500 µL of the channel for each frame of the 5 minute video found in the SI. ∆P (t) and I(t) are shown in Fig. and.