What should I look for when examining fossils under UV light ?

[Brevicollis]

Hello, I'll be on a mineral and fossil convention this weekend, and I dont want to buy any fakes or heavily restored fossils that are claimed to be real. So I'll bring my UV flashlight to see potential repairs. But as I've tested it on my fossils, some pieces that I know are glued didnt show any sign of that, while others were standing out in blue and green tones. Can someone explain me, for what I should look for while examining fossils under UV light, except for green and blue spots ? Is there any way to see plaster or composite parts ? 

If you have any answers and/or examples to that and know, wich glues wont shine under UV light and wich will, please let me know !

Edited May 29 by Brevicollis

[rocket]

look for other colors, lines what are lightning, darker or lighter parts

This will be an indicator for restoration or "fake", but only an indicator!

[hadrosauridae]

You're looking for any inconsistencies.  Fossils are typically rather uniform in appearance, unless some remnant of patternation reacts to the UV.  As for things like bones or teeth, they should generally be a single color.  Glues and paints typically fluoresce differently.  Most of the times, the alterations will jump out as you noticed on some of yours.  The types and wavelength of the light will make a difference also.  Make sure you are using a true UV light, and not a light with a UV filter.  

[rocket]

to show: a claw, original but reglued

you see the different colors from surface and breaking lines

 

 

[rocket]

this crab has some coloration, you see the dark parts

could always be an indicator for restoration, but not always one for "fake"

So, when you see a different color it might be added, but could be reglued or little bit colored. Or, there is a varnish on it, not possible to give a 100% advice

 

 

[Brevicollis]

Thank you so much guys !

That really helps further.