gloves   Speaking from expirience wearing both gloves is definantly a good idea  On the note of safety procedure my friend managed to get a sun burn from the high intensity light  Electrode Cleaning  is commonly performed by grinding shaping the tungsten electrode into a fine burrless pencil point using a high speed diamond abrasive wheel The shape and angle acuteness of the point also plays a role in the focused shape of the plasma arc  The DC arc largely applicable to ferrous metals benefits from using  thoriated tungsten or  ceriated tungsten an alternative to the radiological concerns of Thorium while nonferrous metals such as aluminum and magnesium requiring AC current are performed best with pure tungsten allowing the tip to melt into an enlarged balled surface at the end of the electrode  A ballpoint subsequently flares the arc onto a much broader surface of the material where greater expansion and distortion must then be accommodated or anticipated as part of the welders job  More Cleaning  Theres cleaning or shaping of the electrode and then theres cleaning or preparation of the workpiece to be welded    As you say dirt oil and scale are simply removed from parts for a good weld  Washing degreasing rinsing etc but mechanical abrasion is fast easy and most popular as shaping a weld chamfer can be done simultaneous to cleaning   AlumaPrep or some brand name like that is simply an acid rinse to remove stubborn anodizing and any last marks of finger print oil from the touchy AC needing metals  But as Triddle pointed out in his explanation of  wave form capable machines the plasma itself will often do a fine job of burning off simple surface impurities  Deep inclusions ubiquitous in sand casted work are a frustration all unto themselves  Welder the person tolerance patience and experience must often judge what level of weld quality exist after cooling  Hightech work demands that the work piece billet is good stuff to begin with yet there is a variety of filler rod that can be used to accommodate persnickety base material  Nickle Bronze and Everdure brand name are often blended into filler rods and greatly assist the welder trying to fix cracked engine blocks or other sandy and oil impregnated work pieces  Reactor vessels of all types be they nuclear or cellular are also a field unto themselves  As the physical strength of a finished weld may really be the lesser of engineering concerns  Chemistry plays a role in both questions of what will actually be held in the vessel and how it may be cleaned between use  Low carbon  SS L commonly desired for biomedical applications where autoclaving and bleach will still kick the ass out of Stainless Steel  Titanium and its many grades are like wise a subject for deep thought but once the decision is made  it works like soft butter and few other welds can look so nice raw  As to the safety stuff  A hot horse shoe is hot and most animals with any brain will let go of it before they get burned too bad  Therefor direct and immediate sensible surface heat is far less of real danger than the intense UV of the plasma arch as Gaiusjuliuscesar talked about sun burn often called flash burn  Fully covering any skin just as one might wish to reduce sun burn  Its the same stuff  Welders responsible ones will even clear a room of bystanders even ones who know not to look into the light with out a hood  Side vision looking off to one side doesnt work either as the cornea and retina damage not dependent on center of focused vision is extremely painful when experienced ya I know and not felt for many hours after excessive exposure