So I recently bought a Tilley lamp (my 2nd one), a x246 Guardsman (from 12-1957 as it turns out), and browsing here on the forum to get some info on this model, I stumbled on the term: "speculum plated", like in this topic in the gallery (my lamp in very similar): Tilley X246 Speculum Plated But I'm a bit puzzled what a speculum is? it's not mentioned in the topic "what do I call this part":What do I call this part?: Tilley And googling the word 'speculum' pretty much reveals a medical instrument from which it's best the purpose is not discussed here.... So although English is not my mothers tongue, I was always convinced I mastered it pretty well, but this left me puzzled Can someone explain the speculum? My lamp with his companions in the window sill :
A search of speculum does get you confusing results. I suggest this one as a start. Speculum metal - Wikipedia
Ah thanks. So it's a specific bronze alloy and not a specific lamp part, I've never heard that term. So what exactly is speculum metal plated? is it the fuel cock (looks aluminium coloured but for sure is some kind of brass, judging by the weight) or also the tank? The tank looks chromium plated (also judging by the hardness, I cleaned the spots a bit with fine steel wool and after that a white scotch brite polishing cloth), but I could be mistaken of course.
On the X246 lantern you show it is the tank that is speculum plated. Later X246b lanterns may have been (are) chrome plated, but I don’t know. Tony
Yes I did some more reading on the speculum alloy. Apparently it's quite hard, around 390–440HV, which I didn't expect for a bronze alloy (normal bronze is more like 100HV or 150HV or in that neighbourhood, and used as a bearing metal). Speculum metal 400HV is considerably harder than stainless steel (or normal low grade steel which is even softer) and more inline with prehardened tool steel (or electrodeposited nickel for example). Quite unexpected for a bronze alloy. But a bit prone to corrosion alas I think (compared with electroplated nickel/chrome, although that can also be of very poor quality, it all depends on how it's done). Luckily my lamp is still in reasonable condition. The enamel top is luckily also still free from rustspots so it was probably cared for over it's 70 year life. The glass is made in the eeg, so for sure not original
