The image above shows most examples of different T markings, or lack of them, all in one reference, the 105.012.
I was asked by a complete novice what the T’s on each side of the word SWISS at the base of the dial meant. This is intended as a broad stroke introduction, not an in depth assessment. The majority of Speedmasters covered by this site have T marks. The early watches should not have them, while if later watches do not have them this may indicate a replacement dial.
- T marks indicate Tritium on the dial markers, to comply with legislation introduced around 1963
- T marks were introduced a few years after Tritium was first used – so early tritium dials up to c1963 did not have T marks.
- Once introduced, T marks on Omega Speedmasters are present up until mid 1990’s when Superluminova dials were introduced.
- Superluminova (post c1994) do not have T marks.
- Service dials for early watches, but produced later with Superluminova, do not have T marks
We are also able to make some other statements:
- No 2998’s had T marks. A 2998 with a T dial is a replacement dial.
- early 105.012-63’s had no T marks – this is rare. Some had T marks added after the dial was printed.
- All 105.003’s have close spaced T marks:
- All 145.022’s, all 145.012’s have wide space T marks
Tritium is the radioactive isotope used to cause the markers on a watch to glow and be seen at night. “T” markings indicate the watch contains Tritium, not exceeding a legislated level. The absence of T markings in early Tritium watches is because the legislation had not yet been introduced requiring it.
When the first speedmaster, the 2915, was introduced, the dials were appointed with Radium. Gradually, as the dangers were realized, this was fazed out across the industry and replaced by the safer Tritium. These dials came in around 1961 in the 2998. They were still without T markings, until the legislation required it.
What Tritium is:
Tritium is an isotope of hydrogen, which allows it to readily bind to hydroxyl radicals, forming tritiated water (HTO), and to carbon atoms. Since tritium is a low energy beta emitter, it is not dangerous externally (its beta particles are unable to penetrate the skin), but it is a radiation hazard when inhaled, ingested via food or water, or absorbed through the skin.