You can easily scratch any paint. On black paint scrathes are visible from 20 yards. So the challange is to wash the car such a way that you won't scratch the paint. The other challange is to dry it as quickly as you can so the paint will have a mirror finish.
My viper used to be very dirty. I often run it under rain in very dirty conditions.
This is my secret receipt ...
1. Clean the car with high pressure water before even touching any part with a sponge.
2. Clean the wheels with a "wheel only sponge". I start by cleaning the wheels because once the body is cleaned you have to dry it quickly.
3. Clean the engin if you need.
4. Wash the body again with high pressure water to remove all dust or sand particles.
5. Select a good quality sponge that soaks up a lot of water. Bigger is better. Clean the car with the sponge starting on the top.
6. Rinse the body with a lot of water
7. Dry the body with a good quality shammy. Clean the shammy very often.
8. Detail the engin so on...
9. Once the body is dryed you can use a speed detailer product to improve the shine.
(It is a good two hours job to clean a Black Viper to bring back it to show room shine)
When I have time I use a cleaner wax product to remove dirt that I couldn't wash out.
If you have a lot of scratches you have to use a very fine grind compound to buff out the swirls.
Only professional quality products like 3M will really "repair" the paint (Or sometimes just hide the paint defects).
I have tried all type of products from $5 to $50. They have the same effectiveness ... only professional buffing can repair paint defects.
The best is 3M but it is expensive. I am using Evercoat which is an amateur product. Same effectiveness as 3M but leaves more dust. For a pro the dust is a handicap and slows down the work.
So a year ago, I bought a professional buffer ... and started learning water buffing with 2000 grind paper (on my older race car). Anything else than prof buffing is pure magic and illusion no matter what product you use and how much you pay.
The secret in black paint is the way how you wash and dry your car.
Buttom line is that I know only buy white cars (when I can). My new Viper and BMWs are blue ....
Black is over for me ... until the next deal