What is a critical factor in avoiding contamination of porcelain during dental procedures?

The critical factor in avoiding contamination of porcelain during dental procedures involves handling the materials only during specific stages of the procedure. This practice is essential because anytime the porcelain is exposed to unclean conditions or contaminants, the integrity and quality of the porcelain can be compromised.

By limiting handling to specific stages, dental professionals can minimize the risk of contamination from saliva, blood, or other materials that might compromise the porcelain's surface. This controlled approach ensures that the material remains as clean as possible until it is either placed or finalized in the dental restoration process.

The other options, while they may contribute to a cleaner environment, do not specifically address the timing and context of handling the porcelain itself as effectively as this choice does.