Hello all, online I see a wide range of answers to this question: how hot does an incandescent mantle get while in use? I searched on the site here but couldn't find an answer. I don't have an optical pyrometer, but I suppose that would provide an answer. Any ideas? Thanks.
There is a thread somewhere on CPL that said it reaches over 1000°C. It is certainly hot enough to melt soft solder at a couple of inches - I found that out to my cost one time! I also know of no paint that can withstand the temperature if its applied to a lantern hood despite people trying on a regular basis - not even engine paint. Does anyone have a difinitive answer to this?
It'd be at approximately the temperature of the flame that's sustaining the mantle's glow. That'd usually be somewhere around 1000° C to 1150°C. Seldom any higher due to heat loss and the non-adiabatic conditions of the burn in a lantern. The easiest and surest way to check that is to probe in a type-S thermocouple at the hottest zone of the flame without a mantle. Insulate the bottom plate of the lantern's frame and pump the lantern to the usual operating pressure. Keep the thermocouple in the flame till the tip is glowing bright and long enough for the heat to soak-in at equilibrium state (heat absorbed equals heat dissipated/loss by radiation). Take note that:- The mantle's colour temperature is not indicative of the actual temperature because it isn't purely a blackbody radiation type. The extra luminosity of the mantle's glow is partly due to the 'candoluminescense' effects of its materials. Therefore, we can't use the color temperature chart to provide any indication here.
No-one more so than yourself I think Colin. Testing spray paint products on lantern hoods and Thinking of conducting some explanatory tests for newbies.
For information, there is a paint which the manufacturer states clearly in their technical datasheet, as being capable of withstanding temperatures up to 1000°C continuous . This: Jotatemp 1000 Note that it is still classified as a paint. I have never come across any other paint brands where the manufacturer clearly states in the official datasheet, a product which tolerates this range of temperature continuously . Nevermind the limited choice of colours (gray and aluminium only). I think this is something a little different. Check out the SDS too. Just ignore the solvents. I find the composition interesting. It is not the usual VHT paint with the characteristic siloxane or silane-type binders. I wonder if this one would make it. Note: For any high temp paints, the fillers and pigments are usually highly refractory. They can have fillers like ceramics and other oxides but the thing to check out are the binding resins. They are usually the weakest point in this respect. The first to fail under the heat would be the binders. *** For any high temperature paints, do find out their continuous ratings, not intermittent. Any paint that survives 650+°C continuously also means that it'd survive being heated up to a dull red glow on a continuous basis. A lantern hood will never attain this temperature unless you blast it with a propane torch.
To be brutally honest, I never got around to actually fitting the hood to a working lamp and testing it. I guess I should have but it would have to have been done outside as the smell of burning paint isn't nice. As for the Jotatemp 1000, it's main constituents will (probably) be graphite and carbon in a binding medium. In all honesty, I don't think you could call that paint... a surface treatment, yes, but is it available in bright colours? Will it maintain a colourful surface shine once it's been heated a few times? Probably not. I can, and have achieved the same effect by seasoning the steel in the same way you do cast iron pans. It's quick to do and after two or three treatments you have a long lasting black finish that's impervious to the heat from the lantern. Is it a paint? No, but it works. As for replacing the red or green enamel on a Coleman, Bialaddin, or Veritas hood, vitreous enamel is going to be the only way. One of our members offers this service and although it is quite expensive, the results are very impressive.
I don't think the Jotatemp 1000 is a surface treatment like blackening or phosphating. It isn't a graphite-based coating either. More like a adhering layer of titanium-catalysed-zinc-oxide coating, whatever the binders are. Unfortunately, as usual, these stuffs don't come in vivid, bright colours. They're mostly grey or grey-aluminium. No idea on the gloss level. I don't think its anything like vitreous enamels.
Thanks all for some great responses. The candoluminescence effect is impressive and of course makes these beauties what they are — really rather magical. (Otherwise they’d be like little blowtorches, which are fun but not really magical.). It would be interesting (to me) to learn what mantle temperature is required to start the candoluminescence. I’m always fascinated in watching the mantles come up to temperature and the glow propagates across the surface of the mantle. And here’s another question — in some lanterns (notably the Tilleys I have), there are what I presume to be cold spots — black areas that persist long after the mantle has been at operating temperature for a sustained period and presumably any carbon-deposit from preheating or a flareup has long since been burned away. What is the explanation (and remedy) for these dark areas? If also there are any scientific papers anyone has seen about how a Welsbach mantle progresses from the cold state, through the initial blast, and to the sustained illumination, I’d be very interested in a link. Thanks much!
There are basically two types of the so-called 'dark spots'. First is, what had been caused by real carbon or soot deposits. It is mainly due to insufficient air or too rich a burn. If the mantle is removed, you'd see that the supporting flame isn't entirely blue (various levels of yellows). There are a number of underlying causes leading to that. Worn jet/gas tip orifices, fouled-up generator, incorrect air gap adjustments for certain lanterns, blocked air tubes, stale varnished old fuels are among the common ones. The blackened areas should clear up after a while of burning, provided that the underlying cause is removed. The second type is due to incorrect mantle sizes(usually too large for the specific lantern), inadequate pressures or low fuel-air flowrates, and hence, a feeble flame. Sometimes, it is due to poorly formed mantles, i.e., presence of creases or thick folds in the mantle's weave. There are also some that are caused by poorly-made mantles and those due to 'inferior' mantle compositions. That'd result in lower-than-usual intensities of the glow in those areas. You'd get a lesser glow intensity on those spots. Unlike the first type, these aren't caused by carbon deposits. Candoluminescense is a phenomenon that has been fiercely debated in the past. I don't know if it has been wholly accepted by the mainstream guys or not. Nevertheless, it is a remarkable fact that certain materials, notably the oxides of thorium, yttrium, zirconium, magnesium, calcium and a whole lot of rare-earth elements, emit light, having color temperatures that in a significantly higher range than the blackbody radiation/glow at specific temperatures. In simple terms, the lantern mantles would usually glow with the color temperatures of the equivalent blackbody that is at 2000°C or higher, without actually being at or anywhere near those temperature ranges. You can also do a search on the numerous patents on mantle compositions. You'd find those from the later part of the 19th century and earlier part of the 20th century particularly informative. These include those by Welsbach himself and many others. I had come across some scientific papers and journals dealing on the candoluminescent subject in the past. I'll have a look in my files if any had ever been saved somewhere.
When you say "black areas"; are you are referring to the three dark areas which are in line with the air tubes ? If this is so, the explanation is quite simple, the air tubes must go through to the centre of the burner but in doing so they pass through the stream of gas thus disturbing the flow and causing turbulence which in turn leads to three locations where a slightly smaller flame from 2 or 3 holes in the burner results in a "cold spot".
Super helpful and fascinating reply, Myn! If you come across those papers, I'll be very grateful. I'm finding the technical aspects of these lanterns (I'm an engineer and thus by nature somewhat curious about How Things Work) really compelling.
Henry, that makes entire sense -- and naturally I'd never thought of it! Yes, the dark spots do tend to be more or less in-line with the three air tubes, and thus cold spots ... the Tilleys and Vapaluxes are fascinating to me, very unusual design compared to the things that as an American I saw and used in my lifetime, and (as is true of all design), superior in some ways (e.g., the brilliance of the mantle is not blocked through a considerable arc by generator and air tube), and perhaps less so in others (the top-mounted air tubes seem to be more susceptible to wind than the bottom-feeders). Also I notice that they are unforgiving as to preheating ... there's no faking it with those. Impatience is rewarded with monstrous flareups and (even worse to my mind) a quickly sooted-up globe (right after I'd cleaned it carefully!). Still, I find I'm falling a bit in love with these British lanterns and lamps, with all their quirks ... very nifty items.
While not claiming to be an expert in candoluminescence (I'm a mech/aero engineer), it seems more than reasonable to imagine that a 'apparent' high-K color temperature (which registers optically much whiter than the blackbody temperature/radiant energy would merit) must almost certainly be a candoluminescent phenomenon. That the (somewhat unstable) atomic structure of thorium, yttrium, et al is excited into higher orbitals by sufficient heat and then emit photons in decaying to ground state seems the likeliest explanation ... or a working hypothesis at least ;-)
Schau hier Determine the temperatures, luminosity and pressure and their relationship to each other in a lamp
A convenient experiment to test it to some extents would be to irradiate a burnt-in mantle with a strong ultraviolet light, preferably from sources emitting a fair proportion of wavelengths that fall within the ionizing range. That's to see what are the visual effects of such excitations could bring about. That's also to verify if the materials used on the mantles have such properties(emissions of photons when prior-excited electrons fall from the outer orbits of the parent atoms back into their original orbits). This exists on some known materials but I can't say if it also applies to those used on mantles. There are also some papers and articles on the subject of selective emissions of wavelengths. These articles are usually not freely-accessible from the web. In those, the materials are hypothesized to absorb a large portion of the thermally-relevant, infrared and red spectrum. Very little re-emissions of those,... leading to relatively higher color temperatures as perceived by the eye. It might not be purely candoluminescense at play. Some instance of photon-upconversion process might also be present, especially if there is a small amount of cerium oxide to catalyze it.
Thank you, sir. that is most informative. The temperatures are rather lower than I would have guessed!
