intact c. 1920's wall mount single-sided lithographed tin vitrified clay product chart made for the logan clay products co., logan, oh. vitrified clay pipe is pipe made from clay that has been subjected to vitrification, a process which fuses the clay particles to a very hard, inert, glass-like state. this type of clay is commonly used in sewer gravity collection mains because of its reasonable price and resistance to almost all domestic and industrial sewage, particularly the sulfuric acid that is generated by hydrogen sulfide, a common component of sewage. only hydrofluoric acid and highly-concentrated caustic wastes are known to attack the clay. the chart contains many detailed illustrations, concerning sewer pipes and drains, wall coping, flue lining, etc. the existing surface rust makes the products stand out. measures 18 x 14 inches.