We have built a reactor that allows real-time, in-situ observation of the silicon surface during etching in liquids. We diseuss the issues in etching which it can help to elucidate, and exemplify them by showing a sequence of images of hydrogell bubble formation, growth and motion of the surface of silicon being etched in a KOH solution. We have observed tracks left on the surface by the bubbles. Subsequent measurement witlh a profilometer show that these tracks are made of crates, which implies that pinned bubbles initiate craters under themselvels. The steps in growth of the cavities are discussed.
