Hey @DavidYon47 ,
You won't be able to get a completely shiny silver colour with the conductive ink, even if you burnish for a while. This is because a significant structural component of the ink is not metal, so you'll have a dull shine at best.
You only really need to burnish for 20 seconds at most, after which the ink should be faintly shiny if you hold it up to light. One way to check the difference is to burnish one half of the board for 20 seconds, while leaving the rest untouched. Hold this up to light, and you should be able to see the difference. If you try hand soldering, you'll be able to see a noticeable difference in wetting for burnished vs non-burnished ink.
Hope that helps!