Does it work? Of course, it works, but some people already have the result in their head before they even commence. If you’re convinced, you’ll see nothing, you’ll see nothing. Magick is an art and a science combined.
Necromancy is the process of talking to the dead to gain knowledge about the future. You can see where this is going. The dead don’t talk, neither human or animal, but the Necromancer could, through “dark magic” call back the spirit of the dead person and reanimate the body.
Necromantic rituals could be both mundane and grotesque, depending on their purpose, but they were almost always elaborate - often involving talismans, incantations, magic circles, candles, symbols, and wands. The necromancer might wear the clothes of the deceased, sit for days without moving, or even mutilate and eat corpses as a way to call out to the other side. They would choose melancholy locations that were well-suited to their guidelines - perhaps the home of the deceased subject, a ruin, or a dark graveyard.
All of these morbid practices were just the warm-up for the eventual summoning of the spirit. According to folklore about necromancy, in order to raise a physical body from the other side, the process had to occur within one year of the death, otherwise the necromancer would only be able to evoke the ghost, not the real person.
Some things are wretched no matter the culture. Slavery, rape, murder. These are fundamental sins, and even those who participate in them will usually agree with you, simply coming up with reasons why them doing it is okay. On the other hand, the treatment of the dead is a contentious thing. What is appropriate?
In the modern western world, it’s generally agreed upon that we dispose of the dead either through burial or with fire. We would never eat the corpses of our beloved or make decorations out of bodies. That would be grotesque. And yet, these used to be common and are still practiced in some places.
Eating members of your in-group when they die is called “endocannibalism”, and while it’s rare now, it may have been common in prehistoric times, as suggested by genetic defenses humans have gained against the kinds of diseases you can contract from eating other people.
Necromancy is also known as “Ancestor’s Cult” which was a very common practice in the past. This type of necromancy consists in creating an altar, then investigating a little bit about your family tree, after that, you choose a person from your family line you seek to speak to, and then place some photos of him on said altar, giving some offerings to him.
If you are spiritually awake or at least initiated in the basics of Hermetics you can, with the right knowledge and respect, call forth the spirit of your ancestor, communicating with them is very complicated and the less experienced “necromancers” use tools to understand the spirit’s response.
With time and if both of you feel comfortable around each other, this spirit will help you to get an oracular spirit, that is the main short-term goal of a necromancer. The oracular Spirit is more skilled in the dimension of the dead and can see some events that will take place in the near future, also it can help you to get an operative spirit, this is the one used to seek and summon other spirits, or for more dark purposes, like influencing someone’s thoughts; this is how necromancy (seeing the future, through the dead) is done today.
Is it black magick? Is it good magick? It all depends on the will of the necromancer, just as you can build an orphanage with a hammer, you can kill someone with it.