I know that there is a liquid they sell , you can spray it in your body panel and it shows the imperfection .

Is that a special liquid or can you use anything else at Home Depot , or do a home mix .?
TIA

Hmm .............
Are you talking Guide Coat ?
It's thin spray paint that shows the high and low spots after you do some
initial sanding.

You can just use some rattle can black lacquer, do a light coat, dry, then block sand and you will see the low spots. What little is left over is compatible with most primers.
I don't know if this works with new water based paints.

No , I am talking about a shiny liquid

I'm not aware of a liquid but there is a system with a powder and a big rubber applicator that sells for $35-50. I'm sorry I don't have a name or a pic until tomorrow but it's pretty well known in the industry. Sells on Amazon, eBay and paint suppliers.

powdered graphite guide coat by 3M

http://3mcollision.com/3m-dry-guide-coat-a...-kit-05861.html

Maybe its not graphite but it looks like it.

That's the stuff my body guy likes. Not graphite but good stuff.

I usually use the 3M dry guidecoat for a couple reassons. One is I can get the panel better covered to reveal all low areas or flaws. The other is shelf life. The dry coat (I think is carbon black) doesn't go bad. The aerosol cans can be clogged up when you need to use them.

As a production Painter I used a pre cleaner to sight the panels prior to painting. Use a spray bottle and spray a wet coat on the panel and sight down the side to see any waves or imperfections missed. Then wipe off. PPG used to make DX103 that worked really well and you can buy it bu the gallon. Find an auto paint supplier in your area and ask for some prep wipe or wax and grease remover.

Your probably thinking wax and grease remover. Basically any liquid that doesnt affect the primer will make the panel shiny as ifit has a coat of clear in it.

Old painters trick, but I prefer the guide coat method or feelig the panel with my hand.

Unless someone is an accomplished body man and has the "touch" I would reccomend guide coat with a long block for sure. The use of the prep to shine the panel is a final inspection because there is a definite possibility you will find some imperfections missed or left behind that will need to be corrected. Even as small as sand scratches.
B

As already stated you can use W&G remover if your car is primered. however, if you want to do this on a painted panel, a spray bottle with ordinary water works great. All the waviness shows up!