A perspective on a century of inert seeds in crystallisation

There are many accounts of inert seeds that grow only slowly and fail to proliferate. In the normal course of unseeded crystallisation this results in a latent period between the first cloud point or crystal precipitation and the main crystallisation event. However, similar behaviour has been also observed in seeded crystallisations. Even a smooth precipitation curve may hide periods of nucleation and periods of proliferation within it. Latent periods have often been observed during crystallisation, but infrequently recognised. There are also many reports of critical seed sizes below which they do not bring about secondary nucleation. Sizes between 1 and 900 micrometres have been recorded for different substances under different experimental conditions. It seems likely that the reported failure of small seeds to grow is related to their surface features rather than to their size.