In this column, we’re going to define how “critical” cleaning differs from “precision” cleaning and how each of these differs from what is commonly referred to as “metal” cleaning. Since these aren’t scientific definitions, others will no doubt have different opinions.

My simplest definition of critical cleaning, the aspect of cleaning generally covered in A²C², is like that of the Supreme Court justice who remarked that while he couldn’t define pornography, he could recognize it when he saw it. If you think you’re doing critical cleaning, you probably are.My best definitions of the various types of cleaning, based on details associated with actual cleaning work, are spelled out in Table 1. These definitions are imperfect. I’ve found “metal” cleaning, for example, at a site making instruments via micromachining technology, and “critical” cleaning at a site making kitchen faucets.

Hence the procedures of what is generally referred to as “metal” cleaning may in fact be applied to a plastic used in a stadium cup. Likewise, the work of “critical” cleaning may be applied to a plastic used in optical lens manufacture.

Cleaning isn’t defined by the nature of the substrate being cleaned, but by the process used to obtain the cleanliness.

We teach that some combination of three factors applies to all three types of cleaning: heat or temperature, mechanical force, and solvency. The details of implementation, however, are totally dependent upon the application.