Michael Rath Custom Trombone bell flares offer wide range of tonal characteristics, each material giving a variety and flexibility of sound. They are available in yellow brass (70% copper, 30% zinc), gold brass (85% copper, 15% zinc), red brass (90% copper, 10% zinc) and nickel silver.
The higher the copper content in the material, the darker and warmer is the sound. For example a yellow brass bell will sound more brilliant and brighter than gold and red brass bells with a consistency of tone. Nickel silver bells tend to produce an extremely clear sound, but without becoming excessively bright. When coupled with the right main slide, tuning slide and leadpipe, nickel bells can also sound dark, full and resonant.