and zirconium and aluminum acrylates would be particularly well suited for providing thermal barrier coatings and a surface compressive stress layer additionally layers containing these and other materials may advantageously have different coefficients of thermal expansion than other layers in step 3 appropriate slice data from step 1 is fed to a selective photoexposure device which in turn exposes the layer of build material deposited in step 2 with a suitable actinic radiation according to the corresponding cross sectional pattern derived from the cad model here again it should be cautioned that a perfect correlation between the exposure pattern and the computer generated cross sectional pattern need not be followed hence the term 34 according to the corresponding cross sectional pattern 34 includes both more and less accurate correlations between the exposure pattern and the corresponding cross sectional pattern appropriate intensity and duration of the exposure is contemplated to be established experimentally nevertheless it may be understood that suitable values for these parameters will vary as a function of numerous factors including the nature of the monomers or other polymerizable material the amount and activity of the photoinitiator and the thickness and transparency of each layer to the radiation our experiments have demonstrated that it is desirable for each layer to be cured to a tacky point before adding the next sequential layer this provides a suitable hardness while still permitting adequate bonding between adjacent layers specific exposure parameters are given below but in general it is contemplated that intensity will be about 20 mw per cm 2 in correspondence to the wavelength at which the photoinitiator has maximum absorbance at the surface of the uppermost layer and that intensity will be maintained from about five seconds to about sixty seconds the selective photoexposure device preferably comprises a.