In past years, the sale has raised about $15,000, said Rebecca Massie Lane, the museum's director.
The Singer Society's generosity helps the museum keep admission free, Massie Lane said.
Asked if the museum has considered charging visitors, she said, "We hope we never have to go there."
She said Mr. and Mrs. William Henry Singer Jr. had three requests when they founded the museum -- free admission, public education and a devotion to living artists.
"We've done all three things faithfully for 79 years," Massie Lane said.
She said the Singer Society's volunteer work also contributes to the museum's success -- more than 10,000 hours last year.
Roughly half of the Singer Society's 120 members help put together the treasure sale and preview, Long said.
Friday's three-hour preview included piano music by Wally McClure and a selection of drinks and food, such as garlic shrimp bruschetta or turkey sausage and sweet potatoes.
A silent auction was held for a couch, a piano, paintings, drawings and more.
Massie Lane said about 700 people attended last year's sale, and this year's crowd should be comparable, if the weather cooperates.
"People start lining up at 7 a.m.," she said.
If you go
What: Singer Society treasure sale
When: Today, 10 a.m. to 3 p.m.
Where: Washington County Museum of Fine Arts, Hagerstown City Park