What is a substrate control? why is it done?

An uncontaminated sample is known as a substrate control.  

Explanation:

During the investigation of a crime scene, the forensic scientist collects a sample. This sample helps the forensic scientist to have a better understanding about it.  

A substrate control comprises of uncontaminated surface material near a region where physical proof has been saved. This example is to be utilized to guarantee that the surface on which an example has been stored doesn't meddle with research center tests.

Also, this sample ensures that the surface where the sample has been collected does not interfere with the lab test. The substrate controls enable the background reading about the stained sample.