Making a diminished chord

From Encyc

Constructing

There is an easy trick to making a simple diminished chord. For example, if you are playing a C major chord and you wish to convert it to a C dim. chord. A C major chord consist of C E and G natural. All you must do is bring the third and the fifth down one half step (or make them flat). So then you would be playing C E♭ and G♭ as the chord, making it a simple diminished. You may add the higher C octave to make it fuller sounding. This can be done with any simple chords, such as A minor, B♭ major, B♭ minor, B major, and so on.