I have a ratty X246B that runs surprisingly well in spite of the fact that it is quite rusty. I noticed that the mantle was acquiring a number of pinholes and I believe these to result from loose rust particles falling from the rusty hood above. I decided to take it apart for a de-rust. I used a wire brush on the loose stuff and to discourage the plague coming back I thought some chemical conversion treatment at the rust sites would be worthwhile. I had a choice of some Jenolite, very old and not much left, or some Hammerite Kurust which looked unopened. I picked on the latter. It is thicker than Jenolite and it could be applied with a paint brush and left to soak. I did that, also applying some to the lower part of the vapouriser which was red rusty too. I came back to them around 5 hours later. I had expected that the bare metal/rust sites would be dark - they were. I did not expect the enamel to be affected. It was. Where there was a good quantity of the Kurust sitting as a puddle the enamel appears to have lifted. The vapouriser sat inside the hood (somewhere for it to drip) and it was stuck to the rim by black goo. It was all easily removed but now the enamel is stripey in appearance (no worse than the rust was) but I really did not expect this. I thought it was vitreous and so would be pretty immune to anything like that. I don't think it had been over painted with anything else. I wonder what goes on? Have I accidentally found a way to remove the enamel from hoods? It can't be.
Interesting... These rust converters are usually based on phosphoric acid which reacts with rust to form (black) iron phosphate which is very stable and can be overpainted. Quite how it would withstand the high temperature of a lamp hood, I don't know (or, more likely these days, can't remember). Anyway, I'd have thought the same as you that vitreous (i.e. glassy) enamel would have been unaffected by phosphoric acid - as far as I'm aware only hydrofluoric acid (HF) is capable of attacking glass. Maybe you could blob some Kurust on an old piece of glass and see what the effect is. I think what may have happened with the hood is that the Kurust may have worked its way under the looser enamel surrounding the rust patches and lifted that. Water does that so I expect an acid of any sort would do the same but quicker. The usual way of removing vitreous enamel is by sand-blasting. If there was an easier way, someone would have found it already and be making money out of it!
Haha thanks for your thoughts David they are much the same as mine. I also wondered about the getting under and lifting off theory but it can't explain the black blob effect - what I called goo. The vapouriser end was coated by it when it was left sitting on the hood inner surface but in a shallow puddle of active ingredient. I had to scrape it off. If only I had a camera at the time. I was in too much of a hurry to get on with the job to break off and find one. Not to mention the surprise and how can this be?? The MSDS for Kurust claims the active ingredient is this. 1-methoxy-2-propanol. Also known as Propylene glycol methyl ether. There is one for the chemists. Maybe it is worth trying this a second time to see if it can be repeated.
As mentioned, its basically a rust converter. Well, they almost always contain an acid and at least one wetting agent, which also serve to prime and aid complexing with the base metal. I'm mostly familiar with those containing phosphoric acid and some alcohols(buthoxyethanol and others such as the one stated on Kurust's MSDS). The Hammerite one might not contain phosphoric acid, else that'll be stated in the MSDS as well. Probably a somewhat less hazardous organic acid such as tannic or tartaric? Whichever, its still a reactive acid. And acids will ruin enamelled surfaces. I've deliberately tested milder acids such as citric and acetic on enamelled steel. They will react and dull / matt-up the shiny enamelled surface after just a day's immersion. Found that out earlier on my Milspecs hood. I was initially just as surprised as you were, thinking that most acids wouldn't harm vitreous enamel. Obviously, these enamels are not exactly the same or as chemically resistant as glazed porcelains, which had been fired at temperatures close to the melting point of iron/steel.
As the lamp in question is not from the mid 1960s but probably more like the 1970s I begin to think the hood is not vitreous coated at all. I have been looking up Fusion Bonded Epoxy Coating - also known by the short name powder coating. (seems to date from mid 1960's onwards) I'm not yet sure whether that might handle the operating temps of a hood, but it does say it will coat steel when it is applied at temperatures between 180-250C. Once it has cured it is irreversible - oh yes? Up to what temperature we wonder? Maybe that is what Kurust can attack and soften? If so maybe some powder coating can be found to make repairs to hoods? This one looked OK except where the rust had broken through. Here is a before picture.
John I’ve got 70s and 80s Tilley hoods. They look like they’ve been enamelled to me. I’ll discretely chip one to make sure. David is most likely right about the fluid moving under the enamel. I’ve done the same thing as you (lifting off rusted-underneath enamel) trying to sort out old hoods. Cheers Tony
The date will be stamped underneath the tank. As far as I'm aware, the only deviation Tilley ever made from vitreous enamelled hoods for the X246B was for a brief period in, I think, August 1973 when they were matt-chromed because of energy shortages due to industrial action of some sort - miners' strike, 3-day week or whatever it was. Someone please remind me...
Epoxies are quite chemically resistant to many acids except those hot concentrated nitric, sulphuric or HF. But they are not particularly suited to very high temperatures such as on lantern hoods. At best, they might marginally make it. There are other higher temperature rated coatings available. VHT, etc.
A solution of molasses, 10:1 to 4:1, water to molasses is a cheap; low toxicity, but slow, rust remover. It is used extensively by vintage car restorers whose components tend to be larger than lamp parts. There are videos of the process on the net.
Dave, believe it was "industrial unrest"... something to do with the coal miners, I believe. As a result, I think they rationed electricity for a while during the day.
I've played with a couple of different acids to remove rust from porcelain-enamel finished vents. In my experience, phosphoric and oxalic acid will both etch and fog the porcelain. I need to get some Evaporust to try next, but it's spendy.
@Hippie I’ve used Evaporust on enamelled hoods (vents). It works well, but one still has the issue of corrosion under the enamel resulting in additional enamel lifting off the hood. Tony
