Story about writing with special rare ink to make things happen just the way you wrote it

Question

About 20 years ago, I read a book with a world where there was a special source of ink. It starts with a historical scribe found the source of ink when he ran out of ink and used it to depict the battle of his king. He then noticed that what he wrote happened on the battle field. When he wrote the battle successes of his king(that were a bit "modified from the truth") that actually played out in front of his eyes. When he wrote about successes of the opponent that actually happened in front of his eyes.

I believe the ink was the result of old dragon bodies turning into oil. And that the magic of the dragons got transferred into that oil. Resulting that what was written to become reality, even for a short while.

This led to the formation of a select group of people who knew of the ink, who used it to set up elaborate lives, grant themselves eternal youth, or whatever they managed to dream up/imagine.

The book itself takes place when the ink is running out and all the magical castles are crumbling because they need to be rewritten in the ink every X years to continue to exist.

There was the protagonist, another magician who had written himself wings who tried to steal the protagonists ink because his ink was as good as out, and he didn't want to lose his wings/castle/life.

I believe the protagonist was also meditating on a levitating rock at his introduction to the story. The protagonist used his stash of ink sparingly, which led to him still having enough to perform his own sparse actions of magic.

I believe there were 3 sisters, with two still in their realm and one sister trapped in our realm.(earth, modern day 90's I think)

Another detail I remember, put in spoiler not to ruin it for people.

Somehow the protagonist ends up in our world, ends up having to have sex with a woman in a mental institution(or somewhere else where there's guards) so their bodies are joined, so the sisters can pull her along with him out of the world. Right at the moment the guards break down the door they are vanished.
I believe there were 3 sisters could be more though, with two(or more) still in the realm with one sister trapped in our realm. but I'm really not sure.. it's been 20 years and I was 12 at the time, and no it was not a kids book :-P it inadvertently ended up in the kids section of the library

That's all I remember of the book.

Answer 1

Fiona on goodreads found it: https://www.goodreads.com/topic/show/18313572-fantasy-book-about-a-world-where-magic-happens-by-writing-with-special-i?comment=213485883&ref_=pe_7171740_475466610#_=

Sadly this is a dutch only book, for anyone interested, and hard to get nowadays.

So this book is called: ‘’De Schrijvenaar van Thyll’’. The word ‘’Schrijvenaar’’ caught my attention. That word isn’t used (anymore) in the Dutch language. We use the word ‘’schrijver’’ which translated is ‘’Writer’’. It is written in 1987 by Peter Schaap(I know in the link from goodreads it says 1981, that is incorrect), a Dutch author. As I said he won an award for this book in 1988 at Eurocon in Budapest, the Euro-Award. So, time wise it was written no later than the 90s. De schrijvenaar van Thyll De schrijvenaar van Thyll by Peter Schaap So let me show you where I see similarities in the Dutch synopsis.

The story is about a world where magic happens by writing with special ink.
The ink was found by a historian reporting on a medieval battle and ran out of ink, but found a black substance and wrote with that, found out that if he changed events the battle changed accordingly as he wrote.

So the Dutch synopsis says that an historian, Randoer, finds that when he used dragon scale extract as ink, he could change reality(mentioned in the OP as changing events). The historian became a great sorcerer after that and shared his secret with the guild of ‘’schrijvenaars’’, who guarded the secret closely. Big and lasting changes could only be executed by writing them in seven books at the same time.

Then the story skips forward a couple of centuries and there are a couple magicians who use the ink to live as gods. the ink supply is dwindling and no-one has a big supply.

So it doesn’t mention a skipping couple of centuries in the synopsis, but it says:
One day news arrives that the source of the extract is spent(as the OP says: dwindled) almost completely, as they now use the ink for almost everything. Which causes a big conflict when schrijvenaar Zaranthe(member of the guild of the seven books) refuses to write down in his book, the extract source to be full again(remember that big changes have to be written down in all seven books). With him refusing, since he wants the honour Randoers wish of moderation, all other confreres are outraged.

The hero of the story gets involved with sorceresses which use a different kind of magic, gets chased by other magicians for his supply and somehow he gets trapped in our world on a mission to find a sister who is locked up in our world.

Zaranthe now has to find a magical book, that exceeds all others and makes them powerless. There is no time to lose, since the guild want to write him and his book away to oblivion. Being chased by them and them having more and more grip on his reality, he meets a sorceress/witch Yaraia. Together they fight back.