"And that's just a small fraction," Mrs Underhill said.
"They've been around the country several times now -- and they have to look as good on the very last tour as they did on opening night."
Before working with the RNZB, Mrs Underhill said she had little interest in ballet. But in 1969, while working as a Girl Guide leader, she met Nancy Seaton, a pupil's mother and costumier for the RNZB, who offered to help make the costumes for the Guides' gang show.
The following year Mrs Underhill stepped into her job as RNZB "wardrobe mistress" and was responsible for liaising with designers, budgeting and purchasing fabrics.
Financial constraints meant having to get creative -- with, for example, curtain fabric and appliques from old dressing gowns making a peasant girls' costume.
"We spent a lot of time in second-hand stores and shops that were closing down.
"You had a bit of a squirrel and forage around."
She also supervised the machinists, stitched on the finishing touches, put in zips and sewed on buttons "in a hurry", painted shoes, and dyed hundreds of metres of fabric using "an old- fashioned washing machine".
One of her most memorable moments was the RNZB's season of Swan Lake -- which involved making four sets of costumes for the women and sewing one of the male dancers into his costume seconds before going on stage.
"I didn't have a day off in about eight weeks.
"Look at all those ruffles on the white tutus -- we had to make 24. I used to bring my Guides in, teach them how to use a sewing machine and they'd help with the crinolines."
Mrs Underhill said the RNZB "opened many doors" -- including arranging her a travel grant to the UK, where she worked for The Globe Theatre, the Scottish Ballet and the Royal Opera House.
She also worked for the New York City Ballet, and at Disneyland in LA.
"I didn't get paid big bikkies for it it -- but I met some wonderful people. It was hard work, but I wouldn't have done it if I didn't love it."
The exhibition will be held Thursday, October 1, 7pm, at Club Carterton. Tickets are $10 from Almo's Books.