▁so ▁they ▁stop ▁automatically . ▁In ▁basic ▁automatic ▁p enc il ▁sh ar pen ers , ▁the ▁lead ▁may ▁become ▁too ▁long ▁and ▁break , ▁and ▁so ▁users ▁must ▁be ▁careful ▁to ▁super v ise ▁the ▁operation . ▁ ▁Raz or ▁kn ife ▁ ▁Art ists ▁and ▁craft s men ▁may ▁use ▁a ▁very ▁sharp ▁kn ife ▁to ▁sh ar pen ▁p enc ils ▁and ▁other ▁media ▁free hand , ▁without ▁the ▁use ▁of ▁any ▁mechanical ▁gu ides . ▁For ▁example , ▁the ▁tip ▁may ▁be ▁cut ▁into ▁a ▁triangle ▁shape , ▁and ▁then ▁the ▁edges ▁of ▁the ▁triangle ▁are ▁trim med ▁down . ▁This ▁technique ▁requires ▁a ▁total ▁of ▁ 6 ▁cut s , ▁and ▁takes ▁practice ▁to ▁master ▁without ▁breaking ▁the ▁lead . ▁ ▁Special ized ▁p enc il ▁sh ar pen ers ▁▁ ▁Special ized ▁sh ar pen ers ▁are ▁available ▁that ▁operate ▁on ▁non - standard ▁sizes ▁of ▁p enc il - sh aped ▁markers , ▁such ▁as ▁w ax ▁c ray ons ▁used ▁in ▁primary ▁schools . ▁Sh ar pen ers ▁that ▁have ▁two ▁open ings , ▁one ▁for ▁normal ▁p enc ils ▁and ▁one ▁for ▁larger ▁c ray ons , ▁are ▁fairly ▁common . ▁Sh ar pen ers ▁with ▁a ▁single ▁bla de ▁for ▁use ▁on ▁w ax ▁c ray ons ▁are ▁available , ▁and ▁sometimes ▁included ▁in ▁boxes ▁of ▁c ray ons . ▁These ▁often ▁have ▁pl astic ▁bl ades , ▁which ▁are ▁ade qu ate ▁for ▁the ▁soft ▁w ax . ▁ ▁An ▁artist '