The major disadvantage of cast iron dampers in masonry fireplaces is cracking. The disadvantage of steel is warping. The disadvantage of stainless steel is cost. This English architect designed Trinity Church in New York City and was the AIA's first president. This is usually caused by surface contamination or sometimes by a product formulation defect.
Titanium dioxide is a pigment used in stains.
A white pigment, Titanium Dioxide is used in stains primarily to increase hiding power and give greater brightness. These terms all relate to masonry construction. A good reference for these is the glossary of the Masonry Institute . The answers to this week's puzzler will be published here next week.