The oxide formed during corrosion has an expansive character which induces the cracking of concrete cover. The properties of this oxide layer are focussing the interest due the need to introduce its mechanical characteristics in the models to calculate crack width. In a previous paper it was suggested that the oxide behave as “water” and in consequence it has to be modelled so, which fitted very well in the experiments and model associated an that time. The attribution to the water was based in the observation that the rust has not mechanical consistency and was like a suspension. However, much recent papers insist in attributing other much higher young modulus to the rust. Present paper tries to insist in the original concept by illustrating the formation of the rust in solution and in mortar. The oxides are of mixed colours evolving in function of the time to contact to open air and they have not mechanical consistency, being apparently hydrophilic by retaining large amount of water.