I believe steel started in 1942 and continued to 1945. Ian will likely know more if anyone does. ::Neil::
The way you've got that mantle attached at the bottom looks very odd - as if it's slipped down over the lip at the bottom of the burner spigot; or more likely, it wasn't tied in that position originally. As far as dating is concerned, as Neil says, Ian would know because he saw the factory records before they went to South Korea with the rest of the company in whenever it was - 2008? Has it really been 10 years? I think the change from brass to steel happened in 1942-ish and probably ended in 1945-ish when Willis & Bates began the tie-in with Aladdin Industries of Greenford and Bialaddin was born. Wartime shortages of brass (which was needed for shell casings) is often given as a driver for the change but I think the MOD also probably wanted something more robust (and cheaper?) which could withstand a bit of rough treatment as was likely to occur under war conditions...
Further to what I wrote above, I've checked Ian's book and on page 25 is this, " Towards the end of 1941 as a result of this brass shortage a new model appeared, the Vapalux 300". On page 26 we have, "In October 1944 the slotted collar on the globe cage was replaced by a solid collar with just a triangular aperture for the jet cleaner". Assuming your lantern is fitted with its original collar - and it may or may not be (that's the buggery of refurbishing/restoring lanterns unless 'before' photographs were taken) - there's the end date for the version of the 300 shown above. Given it's fitted with a bakelite jet cleaner knob and assuming that's the original part also, I'd suggest a date later in the range of production - maybe 1943-1944 i.e. mid WW2. I think that's as near as you're going to get...
No need to buy it unless you particularly want a paper copy. Check out Blurb publishing and search for Vapalux, Bialaddin or Ashton. It's all readable online especially when you enlarge the pages...
Blurb Books Enlarge the pages using the arrow icon at the top. You can then read the book in the same way you would a Kindle...
The shown lamp is a Vapalux 300 without the 'X'. The Vapa 300X is a postwar model with a new 'filligrain' ventilator in brass (albeit with the same shape of tank as the 300) that was very short-lived before Aladdin Industries stepped in in late 1946. From then on it became the Bialaddin 300X with the new, more compact type of tank.
