Bob Schroeder, age 15, of Portland, Ore., for his question:

WHAT EXACTLY IS WHITE LEAD?

White lead is a pigment once widely used to make white paint. A synthetic called titanium dioxide has replaced white lead in most house paints, partly because the synthetic performs better.

Titanium dioxide is also safer to use than white lead. Children may develop lead poisoning after eating chips of dried paint that contain white lead. For this reason, the United States government restricts the lead content in household paint.

White lead may be produced by placing layers of sheet lead in earthen pots that contain a weak solution of acetic acid. The pots are buried in spent tanbark, which ferments, producing heat and carbon dioxide. The heat turns the acetic acid to vapor. This and the carbon dioxide acts on the lead to produce white lead.

The powder produced with this method is then ground in linseed oil.