Another one of those products that gets stumbled upon, didn't know existed and yet once you find it, you don't want to be without. I first heard about this from Goss Makeup Artist and he said this was awesome as an eyelid primer. I searched the web and found a few sources but went with Frendsbeautysupply.com. (Not affiliated). It can be known as Dow Corning 244 Fluid OR Airbrush Thinner (but if you search "airbrush thinner", make sure it's silicone based). Those who don't like silicone can stop reading here, but those who don't get reactions to it will want to continue. I have to admit, it did not work well as an eyeshadow primer/base for me. I don't know why. You literally only need 1 drop for both eyes and it will last *forever* but it didn't work well for me in that respect. What it is priceless for though is to revive dried out gel liners, longwearing waterproof shadows (Maybelline Color Tattoo, Hard Candy all lid up, etc...) and for thinning silicone foundations for a sheerer coverage. (I use it on MAC Full Cover). What's nice about this is that unlike the glycerin/primer concoction where you have to heat and mix it into your gel liner or whatever (and it makes a mess, face it), this only needs to be dropped on top and it sinks in on it's own. You can literally drop some on, wait maybe a minute or two and use you product right away. I just decanted some into a little dropper bottle and drop a few drops onto my product whenever they seem stiff or dry. Now I don't have to toss my dried out liners and shadows! I made the mistake of buying 16oz which will last a lifetime, but even the 4oz one at Frends will last a loooong time (and it's under $6).