[Apocalypse]

You talking about when it's all glossy or is it when the edges of the carapace is highlighted around the edges?
Need more info.

 

[Apocalypse]

For trim just use a fine detail brush, dip it in the colour of choice, and make fine stokes of end of carapace.
If ya want it glossy, I think you can buy this special paint wich makes it all shiny. Altough you could use PVA glue since it dries transparent and shiny. I have never used gloss technique myself but I do use the trim effect, looks pretty cool on ma 'nids.