I have had this discussion with a lot of gals recently and so I thought I would just do a post and put it out there. Eyeshadow primer. I have mentioned before that I do not go a makeup-wearing-day without it. An eyeshadow primer or base gives the shadow something to cling to making it last longer and not crease. It also helps the true color of your shadow show through so you don't have to swipe and swipe and swipe to get any color payoff.
A lot of brands have primers but some of the most popular and commonly used ones are:
Urban Decay Primer Potion
Eden - matte finish
Sin - shimmer finish
Original - dries invisible
Too Faced Shadow Insurance
Candlelight - golden shimmer
Glitter Glue - to use with glitter and pigments
MAC Paint Pot
This is actually a cream shadow which dries to a dry finish. Comes in a variety of colors and finishes.
To show you an example I have placed MAC Sketch by itself on the left and over top of MAC Painterly Paint Pot on the right. I put the same amount on both sides, you can see how the base helps the shadow pop.
I have used Urban Decay Primer Potion and find that nothing is going to crease over that stuff! I love my Paint Pots as well as I like the different color bases it provides. I haven't used Shadow Insurance but have read great reviews on it and know a lot of girls that swear by it. This may be a redundant post for many but like I said I've had a lot of questions about primers lately so there are some of you wondering!
I hope this helps and I do strongly recommend you go out and get one! :)