what's this expression?

I think it refers to the occult and gothic trends, like in black magic... Maybe other members will be more helpful...

Zerox"It is a black art, the writing of a history, is it not?" That is how Martha Peake's book begins, but to what does the black art refer? Is it hard to write about history, or what? I would be surprised if it had something to do with medieval times and all the magic that took place at that moment.

I've not read the book, so

Zerox"It is a black art, the writing of a history, is it not?" That is how Martha Peake's book begins, but to what does the black art refer? Is it hard to write about history, or what? I would be surprised if it had something to do with medieval times and all the magic that took place at that moment.

It is nothing to do with mediaevel times. It is

Unfortunately, I can't give more context, since the author has cited that exact part from the book. And I had a tiny oversight; the book's name is Martha Peake, not the writer's.

Black art is defined as witchcraft, sorcery, black magic. It makes sense when the author says: "It is a black art, the writing of a history, is it not?". Sounds like a metaphor to me. I could be wrong because I haven't read the book.

The "black arts" involve the use of sorcery and the harnessing of malevolent powers.

The speaker uses the phrase metaphorically.

MrP

So just to make this sure since this is actually kind of an important issue for me. I would have thought that it means it is hard to write about the history, however, it looks like I was wrong. Therefore, sorry for being a bit stubborn at the moment, but I can't quite understand the metaphorical meaning. Writing about history is just like practising black art, no?[:^)]

Not exactly as metaphor is not direct comparison but simply a reference to another object. You can put it this way: "writing history is like magic", "can be compared to magic", etc. because basically when you're writing something as big and important as that you know it's going to influence people this way or another.

There is also an element of their doing something that is going to have an effect on people, possibly influence their thoughts and behaviour.