The transparent metal coating of a one-way mirror is described as:

A one-way mirror, also known as a two-way mirror, operates on a principle that combines transparency with reflectivity. The transparent metal coating applied to a one-way mirror is designed to be much thinner than that of a conventional mirror. This thinner coating allows a significant amount of light to pass through while reflecting just enough of it on one side to provide a mirror effect.

The key to the functioning of a one-way mirror lies in its ability to retain a degree of transparency on one side, which makes it possible for people to see through it in certain lighting conditions. In practical terms, when the side with more light faces the mirror, it appears reflective, while the darker side can see through it.

The choice of a thicker coating, which is typically associated with conventional mirrors, would not allow for the necessary transparency needed for a one-way mirror's function; hence, such an option would not be suitable. Identical properties to a two-way mirror would negate the unique capabilities of a one-way mirror. Meanwhile, completely opaque coatings would not allow any light transmission at all, which contradicts the very purpose of a one-way mirror.

Thus, the correct answer highlights the specialized construction of the one-way mirror's coating, which is critical for its intended