During discussions of this subject, both Paul Rumpf and Bob Loesch
suggested that the deposit in lead tracker bar pipes would be lead
oxide.  This, I believe is very unlikely.  Any white deposit is more
likely to be lead carbonate.  New bright lead very quickly forms
a thin dull oxide layer which normally protects the surface from
further oxidisation but white lead carbonate sometimes forms,
particularly in damp conditions.

Keith Reedman
Long Eaton, Derbyshire, England