Steam. Get a small hand held steamer and lightly work your way around the cake with it. I absolutely LOVE doing this!
Thanks so some says the shine doesnt stay for long with a steamer? I would need to stay like that for atleast 10 hours as Im making it the night before.
Pearl spray/alcohol mix through an airbrush. I do it all the time. And yes, the steam won't stay shiny a long time.
For a patent-like shine, you can do piping gel mixed with some sort of a thinning agent (haven't done it, but it's certainly not water) and sprayed through an air brush.
*pearl luster dust and alcohol mix, OR pearl spray from a can.
Yes, PME pearl lustre spray in a can or Wilton pearl colormist. Wilton is cheaper though. Steam will not make it "pearly" looking like in this picture.
I would say PME pearl lustre spray for the bow and other white parts but if you spray the whole cake (monkey, coloured dots and all) with pearl it will dull the colours. For the rest of the cake I'd use the PME glaze spray - just confectioner's glaze but in the handy spray can.