Covering.  —  What  is  termed  covering  is  made  by  the  same
formuhe  as  for  the  enamel,  omitting  the  English  rose-red.  Being  with-
out any  coloring  whatever,  it  is  used  for  tempering  the  above  enamels
when  too  highly  colored,  which  may  be  done  by  adding,  according  to
circumstances,  from  one  to  six  parts  of  covering  to  two  of  enamel,  thus
procuring  the  desired  shade.  When  it  is  to  be  used  for  covering  the
base  prior  to  applying  the  enamel,  it  may  be  covered  with  titanium,
using  from  two  to  five  grains  to  the  ounce.
Investient.  —  Take  two  measures  of  white  quartz  sand,  mix  with
one  measure  of  plaster  of  Paris,  using  just  enough  water  to  make  the
mass  plastic,  and  apply  quickly.  The  slab,  on  which  the  piece  is  set,
should  be  saturated  with  water  to  keep  the  material  from  setting  too
soon,  and  that  it  may  unite  with  it.
Memoranda.  —  In  preparing  material,  always  grind  dry,  and  use
the  most  scrupulous  cleanliness  in  all  the  manipulations.  In  all  cases
where  heat  is  applied,  it  should  be  raised  gradually  from  the  bottom
of  the  muffle,  and  never  run  into  a  heat.  Where  it  is  desired  to
lengthen  any  of  the  teeth,  or  to  mend  a  broken  tooth,  it  may  be  done
with  covering,  properly  colored  with  platina,  cobalt,  or  titanium.
