If you use the enhanced client, there is a MOD you can download here
http://vboards.stratics.com/showthread.php?t=167716 that will tell you the intensity value of an item. I've used that and compared it to the information found here:
http://vboards.stratics.com/showthread.php?t=173345
Example, if I find a plate gorget that has 335 intensity and then enhance it with valorite, it will yield a relic. If you find something that already has 401 intensity and you're a gargoyle using the queen's forge, then it yields a relic.
I don't normally play in the enhanced client. I only log in with it to separate out the loot that could be enhanced for relics.
I've only recently downloaded the MOD and have not used it very long. I've found I've been able to produce relics in every case
except if a weapon shows 335-400 intensity and it has elemental damage. Enhancing with valorite does not yield a relic.
I can't eyeball something and know right away that it will give a relic so maybe others can help you in that area.