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acid-free

adjective
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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

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First Known Use of acid-free

1885

in the meaning defined above

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