Figure (c) and (d) are optical micrographs of an interdigitated electrode recorded after 2 and 7 s, respectively (a video is available in the SI). As expected, the silver deposition starts initially on the working electrode. Interestingly, under the experimental conditions chosen here, the silver deposition is observed to grow laterally away from the working electrode. The lateral growth rate was measured to be about 10 m/sec.