residential wiring ?

Actually, solid copper wire is STILL standard for wiring.

sounds right. That would be 12 gauge solid copper.
You do not usually use stranded wire in a house.

Solid copper was right then and it's right now!

The electrician was no idiot.

Asker: You have obviously not been exposed to house wiring before.

Fine stranded, flexible wiring has always been used in automobiles. And it belongs there. It doesn't belong in house wiring. There is coarse stranded wiring, but it's generally used in commercial and industrial building wiring. It's called THHN, and I sometimes use it in houses for pigtails, or in conduit, where it must reside.

Yes, that was normal then. It's normal now too.

What are you expecting? Solid copper wire is still used by default.

I suspect you have 20 amp circuit and # 12 solid copper wire; this is proper and still used today; what is your complaint?

That was normal and the best practice at the time and still is today. Not sure what your concern is. Sounds like you have good wiring. It has lasted a long time and should last for many years to come.

WTF makes you think it is wrong?

Dang copper, cheapscapes shoulda used gold wire!

Yea solid copper is right as long as it is the right size. Stranded wire is junk and not code.

always should be solid wire

PVC insulated cable with solid copper cores is common at that time in the UK.

soft or hard copper is not the matter ,gauge of the wire is important .
The hard wire are pressured and pulled in more process ,but in fact are not good for wiring system ,the wiring system in residential must be flex wire in case of earthquake to not break fast and have flexibility .Houses in 60 till 70's have many errors in structure ,plumbing and foundation designs ,which this year homes are in list of the re build or redo also very hard to get extension to build for these year homes .
If you plan to remodeling ,then just tear the dry walls a part and replace the pipes and wires with new techniques .

Yea thats type wire you want coppers is a good conductor an it does have a big temp variance like aluminum does so connections usually stay tight. An the soild wire makes it easier for the current to pass threw.

Some of the questionable wireing you see could have been done by jack legs that have own the house before you.