An apparatus for producing an object using stereolithography includes a container, a bath of a liquid or powder material filling the container and having a free surface, the material being solidifiable under the action of electromagnetic radiation, a support for positioning the object relative to the free surface of the bath so as to form a layer of the material adjacent to the free surface, a device for solidifying the layer using electromagnetic radiation, a wiper device extending along a first direction across the free surface and drive means for moving the wiper device across the free surface along a second direction. In order to achieve optimum wiping conditions the wiper device has a leading first surface portion and a trailing second surface portion when moving along the second direction, the first and second surface portions extending in the first direction, the first surface portion having a first surface tension value and the second surface portion having a second surface tension value different from the first surface tension value.