4,000 Opera Costumes. 1 Giant Fantasy Sale.

AMSTERDAM — The frog with the skippy ball must go.

So must the resurrected mummy. And the giant ladybug. And that blood-splattered gown.

These items, along with classic doublets, frocks and imaginary creatures, are among about 4,000 costumes the Dutch National Opera has put up for sale to the public Saturday.

Why? Storage is stuffed.

“At some point, the stock room explodes,” Robby Duiveman, director of the opera’s costume, wigs and makeup department, said in an interview Friday. He has overseen three such sales in his 18 years at the opera. But this is the first one the opera has had in nine years.

Pieces of the Dutch National Opera’s recent history — the sweat, drama and flecks of fake blood — may end up at other opera houses or in the closets of avant-garde dressers. The house plans to keep its prized pieces for its archives.

“I never sell the entire production,” Duiveman explained. “We always keep all the principals. If I have 40 chorus members, I sell 30 and save 10. Anything that might be useful for a future exhibition — something from a famous singer, or a world premiere, or something that has a special material — those things I will keep.” “At some point,” he added, “we just have to say goodbye to some of them.”

Known for commissioning interesting, postmodern new work with collaborators such as the artists Anish Kapoor and William Kentridge and the director Peter Sellars, and with a history of both starkly minimalist and classical productions, the Dutch National Opera has an in-house department that builds hundreds of costumes a year.

The costume sales are incredibly popular — the 2,000 available tickets for this one sold out online in 37 minutes. Here is a tiny selection of the fantastical costumes on sale, which date to the 1970s but were used in recent productions.

“The 12-year-old boy who wore this costume had just one entrance on stage, and he just skippied on the skippy ball from stage left to right,” Duiveman recalled. “I remember sometimes he was too enthusiastic and jumped too high, so we had to practice a lot.”

125 euros, or about $160

“This jacket is made of neoprene, which is wet-suit fabric. The great thing about this material is that you can cut it off and you don’t have to hem it; and it doesn’t fringe. And it turned out that when you dyed it, it created this wonderful texture. The opera had a very plain, abstract set, so the costumes became the set, in a way, with lots of these colorful pieces.”

150 euros, or about $190

“A famous German designer once said, ‘When you use details in the costume, they won’t be seen, but if you leave them out, they’ll be missed.’ This little rococo costume was a chorus dress for a pastoral scene, and the fabrics all have leaves and pictures of gardens with shepherds, and the 2-D front panel is made from an image from the rococo period. It might not be possible to see that detail from the audience, but we would miss it.”

300 euros, or about $375

“The entire chorus begins the opera in purple gowns and at the end of the opera, when Ercole becomes the new king, the son god, everyone appears in yellow. It’s a beautiful picture onstage with all these bright yellow gowns.”

50 euros, or about $60

“There’s a scene in which one of the principals goes to the graveyard and the set was a kind of ‘Thriller’ moment from Michael Jackson where all these mummies came out of the coffins and performed this baroque dance number and then go back into their coffins. To make these, the actors came in with cat suits and we had to wrap them up in all these bandages, and then stitch the bandages onto the cat suit by hand.”

100 euros, or about $125

“It’s from a Dutch world premiere that was performed only once. In one scene, there’s a world traveler who is confronted by these slimy men, opera singers, who come up out of the ground and frighten him. The slime is made of silicone. It has an umbilical cord to make them more monstrous.”

75 euros, or about $90

“There is a scene at the end of Act 1 where three guests arrive in disguise and confront Don Giovanni, throwing off their cloaks. Mostly, these days, the costumes are very dark so it’s interesting to see the use of these light, pastel colors, especially with these funny little wings on the shoulders.”

90 euros, or about $110

“This is one of the oldest items we have in our inventory, probably from around 1975. I don’t know what it is because in those days, we didn’t put production tag on the garments. It seems to be a dream-come-true-prince-on-a-white-horse costume. We have several of these in stock, but no trousers.”

100 euros, or about $125

“We had 120 people in this costume onstage at one time, the men with these huge petticoats, all walking down this huge staircase at the same time — very impressive looking.”