Mark plays a yellow brass R10 straight .500 bore with a nickel slide.
It plays nothing like a Williams!!!
I suggest you try a yellow brass 8 inch bell R10 but with a yellow brass slide and nickel slide crook to get anywhere near a Rath/Williams styleD horn.
Oh. I guess I tried too many horns at the ITA Convention last summer. The dual bore .500/.508 Rath that I played was very Williams-like to me, though. That's why I liked it.
How come when I search
I keep getting results saying that Mark helped in the design of the R1?
R1-.500/.510-7.5 Jazz model designed with input from leading jazz trombonist Mark Nightingale, introduced 1996. Dual bore, nickel-silver outer slide.
S.
Yup, he helped develop and started on an R1 which is actually a .500/.510 dual bore and had a rose/red brass bell!!!
He changed quite a while ago actually to the R10.
He still has the R1 which is the prototype but prefers to play the R10.
(Info provided by me, a good friend of Mark's

)