Ultralights , the application of Iridite ( more commonly known as Alodine or Alocrom ) is a chemical cromate conversion process usually applied by brush & paper towel or immersion to provide a corrosion resistant coating to aluminium parts & to provide a base for subsequent protective paint finishes .In my experience , parts which have been previously reworked & coated using the process have on occasion corroded again ( assuming all corrosion was removed in the first place ) . This may be due to the enviroment in which the material is subjected to i.e prolonged contact with corrosive substances ( urine , coffee etc. ), blocked drain holes in stringer/frames , damage to the protective paint finish - around fastener holes in particular , the list is endless . As far as finding info on the process I think ch.51 in the s.r.m.& ch.20 s.p.m. gives details on how & what types to use ( Alodine 600/1000/1200 ). With reference to safety I don't know of any chemical used within the aircraft maintenance game that isn't hazardous so I would err on the side of caution & always wear protective gloves when handling this stuff . Hope this is of some use .
[This message has been edited by Ali Crom (edited 23 December 2000).]