is this a tombac button?

[castletonking]

I'm not sure of this is a tombac button or not

 

[Woodland Detectors]

Looks like it.
Tombac is an alloy formed from a mix of copper (84 - 90%) and zinc (10 - 16%) and sometimes the addition of arsenic which produces a White Tombac. The zinc content is what makes the button surface stay shiny emulating polished silver. Early Tombac buttons date from the 17th century (Pimple Types) but most were mass produced in the Late 18th century most were engine turned on a lathe, others were hand engraved with different themes like hunting scenes & Floral designs probably sold as gift sets, these are allot rarer than the more common machine turned types. On the reverse most have a raised cone shaped base for the soldered copper wire shank the smaller types also shown below tend to have iron shanks ..Generally made for civilian use but also made for the Military of the period. Here is a general selection of what can be found on sites across Britain.