acid–free
adjective
Definition of acid–free
: not containing acid : having a neutral or alkaline pH acid-free paper Every evening, trained volunteers will place any personal items or memorabilia left at the replica wall in archival folders or acid-free boxes. — Brian Burnes, Kansas City Star, 22 Sept. 2010
From the M-W Editors
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1885
First Known Use of acid–free
1885
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