One of the biggest changes in CAD design in the past five years is the creation of models direct from the CAD package using machine controlled tools.

Recently, this design process took another leap forward with the creation of three-dimensional objects or models by irradiation of compositions which crosslink and solidify upon irradiation (photohardenable). This is done by one of two methods, either by solidifying each point individually (by scanning a volume point by point with intersecting beams of radiation), or by building up successive thin layers of a solidified photopolymerizable composition.

Models prepared by this process have been essentially homogeneous in colour and texture. Patent 5677107 describes a new adaption on these methods which produces selected elements which are coloured differently than other elements of the object.

Photosensitive agents that respond at different wavelengths to the photohardenable compound are incorporated into a new mixture. As each section of the object is formed by the solidifying radiation wavelength, the section is scanned with radiation of a different wavelength which selectively addresses the photosensitive agent. This causes the agent to bleach, colorize, or alter the tactile characteristic of a portion of the model.