I bought this stuff because Grant and others said it worked well to remove oils. And it sure does. I suspected that it might be pretty strongly alkaline because of the soapy feel. And I got proof when washing some anodized parts that came in for mods. The Castrol purple stuff started to remove the dye (black) and on the machined surfaces started to dull them slightly. I will still use the stuff on aluminum if I need to but will not let it sit for long. I wonder if it would make a good weld prep for aluminum? ERS
A caution about the excellent Castrol purple cleaner
Nov 18, 2005
7 Replies
I used to clean and etch aluminum parts in a similar highly caustic purple soap (Oakite?) as part of the Iridite process.
jw
It does contain lye, Eric, in which aluminum is highly soluble ..
GWE
Eric R Snow wrote:
I use the purple degreaser myself, in fact I have a 5 gal of it. It is one of the few chemicals in my (home) shop that I use gloves when using. It is very strongly alkaline (lye) and will do a number on your hands just like cement will.
Pete C.
It is so good that the CA air quality folks have banned the sale in SoCal. I am now buying mine in AZ.
Surely it's potassium hydroxide, not sodium hydroxide ? Nearly as much saponification on grease, but a lot lighter on metals.
I'd still be cautious about using it around aluminium. One of the popular bike cleaners (Muc-Off) contains KOH and is known to damage Mavic rims. This says more about the problems with the anodising on Mavic rims than the cleaner though! I'm keeping the cleaner, losing the rims.
Nope, the label on the 5gal of Zep brand purple degreaser I have says Sodium Hydroxide.
Pete C.
Well, there ya go. ERS
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