James Valentine always wondered why a seemingly unremarkable red porcelain pot his great-aunt left him was something special.

But a trip to the Northport Historical Society’s version of “Antiques Roadshow” three years ago revealed his late aunt’s hunch about the piece was right: The West Hempstead resident had inherited a rare 17th-century water pot from China’s Kangxi period, valued at $30,000.

Next month, Long Islanders can find out if their own innocuous tchotchkes cluttering the attic are actually valuable treasures at the society’s next Antiques and Art Appraisal Day.

Participants may bring up to two items for appraisal at the Nov. 5 event, which will be held at Northport Village Hall.

Officials said they will only be able to appraise 100 items — potentially raising $3,000 to $4,000 in appraisal fees if all the time slots are booked.

The event replaces the society’s annual antique show, which had seen attendance — and revenue — decline in recent years, said Steven King, president of the society’s board of trustees.

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In 2012, the show attracted 850 people and raised $4,900, but by 2015, that had declined to about 700 people and only $1,800 in revenue, King said.

Society officials decided it was time to try to revive the appraisal approach to fundraising for the nonprofit, which has an annual budget of $125,000.

“There’s a big change in how people acquire antiques, because now, of course, there are online auction houses,” King said. He added that a stand-alone appraisal event also eliminated the cost associated with renting out space for a large antique show — especially since the society was able to use Village Hall for free.

King said an appraisal event also has the potential to seize on the growing public interest in finding value in unexpected objects — as evidenced by the popularity of PBS’ “Antiques Roadshow” and other, similar programs.

“The contrast is that you’re not coming to buy something — you’re coming to show something you already own,” King said.

That was the case with Valentine’s unexpected treasure. The small, wide pot with a narrow mouth, in a shade that experts describe as “peach blossom,” was the most valuable item ever seen at the historical society’s two previous appraisal events in 2009 and 2013.

“I was completely flabbergasted,” Valentine said. “It was unbelievable. If you saw a picture of this pot, you wouldn’t think it was worth anything.”

“Antiques Roadshow” expert Lark Mason, who had appraised Valentine’s pot and is again volunteering his appraising skills at the society’s event, said people are drawn to the possibility of unlikely treasures in their own home.

“It’s trying to unravel a mystery,” he said. “The thing that’s really joyful about what we do is to find things that have value that someone is unaware of, and to be able to share that with them. In some instances, it dramatically changes the person’s life.”

For Valentine, who in May 2014 sold his great-aunt’s piece on Mason’s iGavel Auctions website, the life change was tangible — if not antique.

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“I got a big Buick LeSabre,” he said. “Brand new, shiny car.”