Washington: We worked at chemistry
The 35-year-old told Los Angeles Confidential magazine: "What you see with Jamie and me - it's rare.
"But it comes from a whole lot of crying, a whole lot of sharing, a whole lot of blood, sweat, and tears."
The film follows Django (Jamie), a freed slave who treks across America with bounty hunter Dr King Schultz ( Christoph Waltz), and Kerry plays Django's wife.
Kerry, who starred in The Last King Of Scotland, also opened up about being a black actress in Tinseltown.
She said: "My grandmother was a maid on Park Avenue and her grandmother was a slave. The expectations about what's possible for African Americans is always shifting and always growing, but Jamie's right: If you're black in Hollywood, you have to be twice as good and work twice as hard as everybody else."
Django Unchained, which also stars Leonardo DiCaprio, is due for release in the UK in January.