Cause of Carpet Stain


A stain in the carpet in a South Carolina courthouse seemed to reappear and grow in size after every cleaning. So persistent was this mysterious stain that it had been nicknamed “Ralph.”

Analytical testing of stained carpet by light and electron microscopy


Light microscopy aided by scanning electron microscopy (SEM) showed that Ralph was actually a discoloration of the carpeting caused by small particles adhering to the carpet fibers. The stain was not caused by growing mold or soot, a concern of the occupant of the office, but by particles typical of what might be found in indoor environments: fungal material; glass, cotton and paper fibers; starch and some construction debris.

The analysis also showed that the particles were stuck to the carpet fibers by a dark, sticky, resinous material.  Analysis of this material by micro-Fourier transform infrared spectroscopy (FTIR) showed a very close match to corn syrup.


Ralph was probably caused by a spilled soft drink. While cleaning apparently removed the surface dirt causing the discoloration, it was not thorough enough to remove all of the dried corn syrup from the drink. Some of this sticky material was spread with the cleaning effort and then simply attracted more dirt. Thus Ralph grew each time he was washed.