and fewer angular discontinuities than the pores or openings in conventionally manufactured shells that are otherwise identical but use angular salt crystals rather than rounded salt crystals as will be shown this difference surprisingly leads to statistically significant changes in overall shell strength in one embodiment the rounded salt crystals are applied so as to achieve a depth ranging from a portion of one crystal diameter to a multiple of many crystal diameters the crystals may be embedded in the surface of the shell to a depth of from about one to about three times the diameter of the crystals penetration of the solid crystals depends upon the size of the crystals the thickness of the final uncured layer the viscosity of the uncured layer and the force with which the crystals are applied these parameters can be controlled to achieve a desired depth of penetration for example if the last layer is relatively thick and low in viscosity less external force will be required on the solid crystals to produce an acceptable pore depth although standard sodium chloride is preferably used for the rounded salt crystals other salts may be suitable based on several factors 1 the salt should be economically available in the desired particle sizes 2 the salt should be nontoxic in case some remains in the surface of the prosthesis and 3 the salt should be readily soluble in a solvent that is economically available nontoxic and does not.