I've just been experimenting with a Colorstar 3000, and from reading the Frances Schultz article on the Colorstar I need to calibrate the machine with a colour negative of a gray card, not included with my example. So my question is: what are most appropriate methods to create the negative? My initial thoughts are to photograph a gray card under my 5000 K CRI 98 tubes (4 x 58W ceiling mounted in a small room) with a neutral film such as Kodak Portra 160 NC. However I'm sure there are other considerations that I should take into account...

To show my chemicals are okay (freshly mixed Fuji RA-4 Xpress) I've included a very quick scan of an initial attempt:

Film: Kodak Portra 160 NC
Paper: Fuji Crystal Archive
Development method: Nova slot tank