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I have some oil-pastel sketches on newsprint I would like to treat for framing (and longevity). My plan is to rinse them in a deacidifying bath, then use wheat paste to wet-mount them to heavyweight pH-neutral 100% rag paper. And finally, to frame them with UV-protective glass recommended for art.

My question is this: Is there any reason not to use baking soda for the deacidifying bath?

I have experimented with it, and it seems to work great. I used a garden-soil pH test solution before and after, and sure enough, the treated paper shows no sign of acidity. The wheat paste bond seems just as good with the treated newsprint as with the untreated newsprint. The oil pastel colors seem unaffected (not surprising, oil pastel being very water-resistant).

Is there anything about sodium bicarbonate that might, over time, cause a visible effect on the paper?

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It seems that adding bicarbonate is how acid-free paper is made, though more modern paper is neutralized by the use of chalk as filler. The wiki page says that magnesium or calcium bicarbonate are commonly used, but that may be just due to cost rather than any specific issues with using sodium bicarbonate. Source

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  • $\begingroup$ Aha! The Wikipedia page on acid-free paper says that as the magnesium or calcium bicarbonate deacidifying solution dries it leaves a carbonate residue. Presumably that means that using baking soda would leave sodium carbonate? Sodium carbonate is apparently hygroscopic, which could cause paper to buckle or mildew. And that's a very good reason not to use baking soda to deacidify paper! $\endgroup$
    – Laura W
    Sep 11, 2014 at 7:27
  • $\begingroup$ >Presumably that means that using baking soda would leave sodium carbonate? || Yes, it would. In case you really care, consider ammonium bicarbonate or aqueous ammonia. But it STINKS. $\endgroup$
    – permeakra
    Sep 11, 2014 at 7:48
  • $\begingroup$ You can always try it on something you don't care about and see if it's actually a problem, or there's the option of just rinsing well with DI water to remove any remaining bicarbonate after you've neutralized the acid. $\endgroup$
    – Michael DM Dryden
    Sep 11, 2014 at 16:25
  • $\begingroup$ I am hoping not to have to subject the wet newsprint to too much manipulation -- the sheets are large and rather fragile while soaking wet. I am going to try one of the other bicarbonates next, maybe calcium. $\endgroup$
    – Laura W
    Sep 11, 2014 at 16:43
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As the sodium bicarbonate solution dries, it gives off carbon dioxide and water, leaving a residue of sodium carbonate. Sodium carbonate is hygroscopic, meaning it will attract moisture from the air. Moisture can cause paper to buckle and mildew, and that is good a reason not to use a baking soda bath to deacidify newsprint for archival purposes.

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  • $\begingroup$ I thank @Michael for the reference to the Wikipedia article on acid-free paper. Somehow, in all the reading I've done about deacidifying newsprint, I missed that article. Reading it and then looking up sodium carbonate is what gave me the answer. $\endgroup$
    – Laura W
    Sep 11, 2014 at 16:21

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