Opinions requested on lume from circa 1960 for 1675

[georgetownhoya]

Hi sensui - congratulations on a beautiful watch! That watch actually was found by me. I bought it from the friend of the original owner who inherited it in the mid-1990s after his friend passed. I was offered the watch by e-mail after the gentleman saw the Reference Points video and article on HODINKEE and spoke with the elderly gentleman who owned it for hours about the watch, which was essentially unworn and untouched since he received it.

As others have mentioned, there is a run of GMT-Master reference 1675 examples with that greenish, long-glowing and low-to-no radioactivity luminous material, typically with an inside case back production of "IV.60" (meaning the case was made in the fourth quarter of 1960, with the watches being assembled and tested well after that). I believe that this lume mixture on this run of GMT-Masters, as well as the "Tulip" or "Tulipino" Submariner reference 5512s was strontium aluminate. Here is how Wikipedia describes it: "Strontium aluminate is an aluminate compound with the chemical formula SrAl₂O₄. It is a pale yellow, monoclinic crystalline powder that is odorless and non-flammable. When activated with a suitable dopant, it acts as a photoluminescent phosphor with long persistence of phosphorescence."

Alex Ciani recently wrote this on Instagram: "It’s common knowledge that tritium replaced radium as the luminous paste on watch dials in 1963. It wasn’t however the first less-radioactive material to be used for this purpose: starting around 1960 Rolex had already been using - alternatively to radium - strontium aluminate, a mineral based compound still used today for many applications. Those dials are easily recognized by the vibrant, greenish color and intense luminescence, something that has often misled the judgement of many vintage watch experts back in the day, with the consequence that a number of perfect factory dials ended up being “relumed” with very questionable results."

If you have any questions, please feel free to reach out to me. Eric Wind of Wind Vintage