Book of Secrets... **Spoilers**

[⎛Double Double⎞]

When I put the Book into the Core it changes color... I have put 2 books in so far... I know it can boost a relic but what is the best way to use the core? Should I keep throwing books in? Whats the right strategy so I don't waste it on something.

[Gorgosian]

I have tried all the combinations and waisted more time than I wanted to, to find out what I don't need at all and the following lines still remain a possible recommendation and not a "must be".
Please feel free to play your own game.

As soon as you put the first book in the core, it turns blue = Corrupted core
After puting another book it will turn yellow again and you have the divine book of secrets in your relics' bag.

Lots of spoilers ahead.

Now you put the divine book in the core and the core turns divine.
Whatever you throw into it will now be divine warped (Relics, Weapons, Scientists).

Warping scientists in a divine core works only for legendary ones = Warped++
All other scientists can only be warped in the corrupted core = Warped+

Most worthy:
1- A few book of times.
2- Maybe 2 Fuel tanks in combination with Superminer Toth (caves become easy).

Hint:
Some players as I do too, use 10 divine golden scythes++
The scientists will always be resurected.
What if you have the wrong scientist and you want to change to another one?
In that case you throw the scientist in the core and the scythes will resurect him/her again.
Proceed until he/she really dies.
Now you receive automatically a new one.
Proceed until your favourite scientist appears.
This one will be at level 1 and needs to be warped again.

Waisting books of secrets:
All you can get in the buff lab doesn't need a relic in the the bag - btw the buff lab gives a higher boost for a long period.
Weapons: Your fighter is strong enough to deal with all the monsters - as long as you upgrade his weapons continuously - besides he gets stronger with each depth level.
Book of success: Solution = 10 golden scythes++ = Scientists at level 100+
Midas touch: Doesn't give as much as expected unless you have at least 4 warped++
Bag for capacity = You will alwayss be short of capacity anyway and that's good, because you sell the excess considering you need the money anyway.
Juicers: Just upgrade the superminers.

[76561199485685767]

Book of Secrets
This is a very rare Relic (second most rare in the game, and since you will need a few, the most needed).

The main source is scientists' excavations. It can be gained sometimes in the Trading post (usually at a very high price, not affordable at all, especially when it's on materials, although sometimes you can make do with Material sacrifices. It cannot be gained in any other way (no chests, no quests, no tickets).

The Book of Secrets has no use other than to be sacrificed into the Core.

Abridged version
Toss a BoS in the core, the core gets blue
Toss BoS at the blue core, you get warped BoS
Toss warped BoS at the core, the core gets divine
Toss any relic at the divine core and it has a 50% chance of becoming a divine relic
Core changes
The Warped/Divine changes to the Core do not affect the sacrifice of minerals. It only affects relics and scientists.

When you sacrifice the Book of Secrets to a basic Core, it corrupts/warps it (this is shown by changing the base yellow/red color of the Core to blue).

If you sacrifice another Book of Secrets to a corrupted/blue Core, it gives back (100% rate, this is an exception to the general rule) a Warped "Book of Secrets+". The Core turns back into a basic core.

If you sacrifice the Book of Secrets+ to a base Core, the Core becomes blessed/divine (golden).

DO NOT SACRIFICE a Book Of Secrets to a Divine Core!!!. This will have the effect of changing back the Blessed Core to a Warped Core, thus wasting two Book of Secrets.