This is a video of a digital artist restoring an old black and white photograph to color. This used to boggle my mind a few years ago when I saw it done for the first time because I had absolutely no idea about Photoshop and how it worked, it just seemed like a mystery to me.
From what I can tell, he does most of the scratch & wrinkle removal right on the background layer with the clone stamp and healing brush tools. It’s almost mesmerizing watching him move around the image and fix everything, but it’s painful too because I know would do something like this on multiple layers or at least a duplicate of the background in case of mistakes.
When he starts colorizing he makes a set of color layers corresponding to different skin tones that would likely be in the image, masks them in, and uses soft light for a blend mode. It looks very simple when explained but this type of retouching is almost an art form in itself and is made easier with a tablet. I don’t know if this artist uses a Wacom tablet or a mouse but, just from personal experience, almost every tool in Photoshop is made easier and more fluid when used with a tablet.