after reading https://www.wikihow.com/Clean-a-Keyboard and other sources I used a 75% isopropyl alcohol solution to clean my black and grey plastic notebook's keys and surface.
I applied the alcohol to cotton pads. Each cotton pad I used came back black, completely black. This is the first time I use isopropyl alcohol to clean this notebook I bought it 8 years ago.
To clean the surface I sometimes pressed the pad with my nails, because I first thought the black residue on the cotton pads was simply dirt and oils accumulated during 8 years. Now, on second thoughts, it could be the isopropyl alcohol solved the upper layer of plastic and now the clearer lines I see where I pressed with my nails are how the notebook looked 8 years ago. Lines look like an anarchic groove, but don't feel different to the finger.
On other parts I can also see the circular motions I applied to clean those parts. Do I have to apply more alcohol or have I already damaged the plastic?
OTOH I cannot believe wikihow and other sources like https://www.howtogeek.com/65073/how-to-thoroughly-clean-your-keyboard-without-breaking-anything/ would include information that hurts the computer.
Am I doing this right?
Isopropyl alcohol can damage plastics. I prefer distilled water for surface cleaning.
note that this damage is not necessarily in the form of dissolving. it causes some plastics to develop fractures, as if you had dropped it. dont use iso on plastic unless you know it is a kind that it is safe for.
BTW, i just just want to plug for this fact: we are all totally brainwashed by marketing that we need special cleaners for each specific thing. dishsoap or some general purpose soap like Dr bronners and water works fine for just about everything.
Oh that's a good call. I've been using some gentle lens cleaner spray
Some plastics get gummy and start to disintegrate as thet age. You might be rubbing off the aged/oxidized plastic.