I clay mine twice yearly,the first claying I do is usually the toughest one....it's the one that seems to have the most contaminates...mostly tree sap and atmospheric fall out; city pollution,pollen, sweet water....the stuff the clay bar picks up is just unreal....this is AFTER you washed your car!!!!!! it just goes to show you how much "crud" is left on your paint work!...after that first through claying, sealing and waxing, I find most if not all pollutants just DO NOT really stick to bright coach work, as long as a high quality sealer/ wax is used.
One tip I share tho: the first time I clay, the initial wash is done with almost hot as opposed to cold water....it completely softens the minuscule droppings of sap, and by and large, allows the shampoo to actually remove them...I find that after I washed with almost hot water, and air blown the coach work, the clay removes 99.9 of crud very easily.
As a general rule, I try to NEVER park ANY car underneath ANY tree, and any sap I find attached to the paint is quickly removed before it has time to set and harden.
As far as black paint is concerned.....never ever wash a car in circular motion EVER,it's the NO#1 way to create swirls....fine particle ambient dust that has settled on the paint is now emulsified with a thickening agent (shampoo) and water ( carrier) creating the perfect identical ultra fine cutting compound.....I know this sounds crazy,but if you use a jeweller's Lupe and take an enlarged look at what a swirl looks like ( in full sunlight) you'll suddenly notice they are ultra fine "groves that have been cut into the top layer (clear coat) which is why to fully remove them, either a polisher with ultra fine compound or a water sanding using a 5,000 cutting grit!
"Automotive Sandpaper can come in a variety of coarseness from about 40 grit which is the most abrasive up to 5,000 grit which is not much more abrasive then a regular sheet of paper in your computer printer. Each piece is exactly the same as the last that way if you are sanding down an imperfection in the clear coat you can grab a 3000 grit paper and know you won’t be cutting through the clear into the base coat.".....
I stick with the 5,000 grit because it is just sooooo fine!...I did a friends Viper last year (black) that looked completely trashed! never seen so much swirls on ANY car....lol he used to drive it through a roller car wash....we worked on that paint for 2 days straight using 2, 45 degree angle floods to highlight the severity of the swirls before we got to sealers and waxes....the end results were just incredible!....he also used to dry it with a synthetic chammy....compressed air is the only way to go, just blow the water right off it.
Black, as my general rule is my fav colour....but just too delicate for my liking.....never again! lol