Thin layers of what metals are used in the Vacuum Metal Deposition process?

In the Vacuum Metal Deposition (VMD) process, thin layers of metals are applied to surfaces in a vacuum environment to enhance the visibility of latent fingerprints. Gold and zinc are specifically chosen for their unique properties that contribute to this forensic technique.

Gold has excellent conductivity, corrosion resistance, and adherence properties when applied as a thin film. It allows for a high-quality deposition that can reveal hidden fingerprint patterns effectively. Zinc, on the other hand, serves as a support layer which helps in binding and enhancing the contrast of the fingerprint ridges against the background. The combination of these two metals enables the visualization of latent prints on various substrates, making them ideal for forensic analysis.

The other metals listed in the options do not possess the same effectiveness or suitable properties for VMD. For example, iron and copper do not provide the same level of contrast and quality needed for clear fingerprint visualization. Similarly, silver and lead, while used in various applications, do not combine the right attributes necessary for VMD processes. Lastly, aluminum and nickel, while they can be involved in different kinds of metallization processes, do not serve the same specific purpose in the context of latent print development as gold and zinc do.