glass vs. varnish for acrylic paintings

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Ok so I am trying to enlighten myself on the issue of painting conservation/ preservation. I know that it is suggested to varnish oil paintings after about 6 months to let them dry and to not put them under glass. Or at least that's what the internet says. What about acrylic paintings? I put mine under museum glass to avoid varnishing and or spraying fixative on them because I don't want to alter them in any way. Is this the best way to preserve them? For over a year I have been talking to people and searching the internets for one answer to no avail. Everyone says something different. I know that varnish protects them from dust, dirt, smoke and light but doesn't glass do all of that as well? Is it necessary to varnish paintings if they are under glass, especially acrylic paintings? If you know please let me know . I hope this is the right board for this..

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