Ink for jet recording and ink set

An ink for ink jet recording, which comprises a dye having:

• a λmax in an aqueous solution of from 390 nm to 470 nm;
• and
• a I(λmax+70 nm)/I(λmax) ratio of not more than 0.4, in which I(λmax) is the absorbance at λmax and I(λmax+70 nm) is the absorbance at (λmax+70 nm), the dye being dissolved and/or dispersed in an aqueous medium, and the dye is represented by formula (1),
• A-N═N-B (1)
• wherein A and B each independently represents a heterocyclic group which may be substituted,
• wherein the ink has a forced fading rate constant of not greater than 5.0×10−2 [hour−1], in which the forced fading rate constant is decided by printing the ink on a reflection type medium, thereafter measuring a reflection density through a Status A filter, specifying one point having a reflection density (DB) in an yellow region of 0.90 to 1.10 as an initial density of the ink, forcedly fading the printed matter by use of an ozone fading tester that can regularly generate 5 ppm of ozone, and determining the time taken until the reflection density reaches 80% of the initial density, and
• the total amount of a cation in said ink except for a monovalent metal ion, a hydrogen ion, an ammonium ion, an organic quaternary nitrogen ion and an ion produced by the proton addition to a nitrogen atom in a basic organic material is 0.5 wt % or less.