We investigated the influence of catalyst preparation on the growth of coil-shaped nanotubes by varying the pH of the solution during catalyst impregnation, to elucidate their formation process. The spirals were observed by transmission electron microscopy, and we determined the dimensions of these coils for a large number of them, to compare them to straight nanotubes, and also to establish correlations between these dimensions and catalyst preparation. We also looked for the nature of curling at the nanometer scale. A growth mechanism for these spirals is finally suggested.