We present magnetic resonance images of the formation of an alginate gel as calcium ions diffuse, through a dialysis membrane, into a sodium alginate solution. Instead of conventional magnetic resonance imaging in a high magnetic field, we employed the electronic Overhauser effect in an imaging mode to enhance the proton signal at a field of only 16 mT. The high sensitivity of the Overhauser effect to small changes in mobility permits to monitor spatial inhomogeneity in the very early stages of the gelling process.