174
CHAPTER  XI.

OF  BLUE,  AND  OF  BURNT  YELLOW.
BLUE  was  first  manufactured  at  Alexandria,  and  afterwards -
  by  Vestorius  at  Puzzuoli.  The  method  of  making
it,  and  the  nature  of  the  ingredients,  merit  our  attention.
Sand  is  ground  with  flowers  of  sulphur,  till  the  mixture

is  as  fine  as  flour,  to  which  coarse  filings  of  Cyprian
copper  are  added,  so  as  to  make  a  paste  when  moistened
with  water;  this  is  rolled  into  balls  with  the  hand,  and
dried.  The  balls  are  then  put  into  an  earthen  vessel,
and  that  is  placed  in  a  furnace.  Thus  the  copper  and
sand  heating  together  by  the  intensity  of  the  fire,  impart -
  to  each  other  their  different  qualities,  and  thereby

acquire  their  blue  colour.  Burnt  yellow,  which  is  much
used  in  stuccos,  is  thus  made.  A  lump  of  good  yellow
earth  is  heated  red  hot;  it  is  then  quenched  in  vinegar,
by  which  it  acquires  a  purple  colour.

CHAPTER  XII.
OF  WHITE  LEAD,  VERDIGREASE,  AND  RED  LEAD.
Ir  will  be  proper  to  explain  in  what  manner  white  lead
is  made,  and  also  verdigrease,  which  we  call  æruca.
The  Rhodians  place,  in  the  bottoms  of  large  vessels,  a

layer  of  twigs,  over  which  they  pour  vinegar,  and  on
the  twigs  they  lay  masses  of  lead.  The  vessels  are
covered,  to  prevent  evaporation  ;  and  when,  after  a  certain -
  time,  they  are  opened,  the  masses  are  found  changed
into  white  lead.  In  the  same  way  they  make  verdigrease, -
  which  is  called  æruca,  by  means  of  plates  of