Anyone Know If Vintage Brown Kraft Envelopes Are Acid Free?

Coinfrog:

Thanks! I get so many in old brown small envelopes that look Kraft from old estates, and you see so many listings for coin envelopes, like this below (no idea who the seller is, just an example) that use Kraft in the name and say "Coin Envelopes". I probably, if I did use them, should just write "not for permanent storage" on them at the very least. Plus half the time regular plastic bags for bulk coins are not acid free and the small acid free ones are just not large enough. Anyway, thanks again!

https://www.ebay.com/itm/1-Coin-Env...AOSwsMVZdn6j

OK looking up the original "Kraft Process" you get

-->Kraft Paper: Paper formed of pulp created by cooking the wood chips in liquor made chiefly of sodium sulphate. The resultant pulp may be bleached or unbleached and is noted for its strength of fibre. When applied to pulp, the word kraft is used interchangeably with the word sulphate.<--

So you have, originally and if unbleached, an alkaline process. Now too alkaline is probably as bad as too acidic, but at least we are on the high side of the pH when they make these.

My understanding is that vintage modern paper (i.e. made from wood pulp rather than cotton or linen) is unlikely to be acid-free (the woman sitting next to me worked in library conservation for some years). That said, I have no idea how acidic paper must be before it becomes detrimental for storing coins.

Sources of acidity in paper
During manufacturing

Papermaker's alum Al2(SO4)3.18H2 O
Added during the manufacturing process. Dissociates in water to form sulfate ions and hexaaquaaluminium(III) ions [Al(H2O)6]3+ that can undergo acid hydrolysis.
[Al(H2O)6]3+ + H2O #8652; [Al(OH)(H2O)5]2+ + H3O+

During storage

Nitrogen dioxide
An air pollutant that can both form nitric acid on reacting with the moisture in paper and oxidise the hydroxyl groups on cellulose fibres to carboxylic acids, increasing the acidity of the paper.
3NO2 + H2O #8594; 2HNO3 + NO
Cellulose-CH2OH + 2NO2#8594; Cellulose-COOH + 2NO + H2O

Sulfur dioxide
A pollutant that can form sulfuric acid on reacting with the moisture in the paper. This reaction can be catalysed by the presence of certain metals (eg manganese) that may have been introduced in the paper making process, probably by oxidation of the dioxide to trioxide.
Handling

Lactic acid
A component of sweat, lactic acid is a weak acid that can transfer to paper surfaces during handling.
https://eic.rsc.org/feature/paper-c...0204.article

I do agree that if the Kraft paper is made using sodium sulfate solution instead of alum, this at least removes one of the possible sources of acidity as the Na2SO4 liquor should be neutral vs the acidity of the hexaaquoaluminum ions in alum solution.

Also found this comment:

Kraft paper has not been made with acid sulfite since the 1930s. It is the only paper made in a pulping process to be free of acid sulfate. Subsequently, lignin is removed during the kraft pulping process. Kraft paper is neither the same quality nor as acid-free as the more expensive rag papers but it can be safely used for wrapping food and for many archival purposes. Auction and storage houses regularly use kraft paper to wrap silver because its lack of acidity prevents tarnishing. If you still have doubts you should perform a litmus test after soaking a sample in some distilled water.

From the first reference, older modern papers of any kind should be more likely to be acidic than new paper because of more absorption of acidic pollutants from the atmosphere.

Older Kraft have a more dominant sulfur content. They tone coins dark (not pretty). A silver coin left in one for a few years will be nearly black. I'm sure that type of "toning" must have an effect on the coins surface.

I've bought a number of collections "back in the old days" and I always took out every coin in Kraft as soon as they were mine.

The only advantage to them is that they give you a large writing area which is especially useful with ancient coin descriptions.

I tossed my boxes out many years ago and I've never missed them.

The sulfur in Kraft paper envelopes imparts a nice toning on silver coins over an extended period of time, especially in sunlight, but high humidity will cause ugly black spotting instead.
However, the longer the empty envelopes are exposed to air, the less reactive they become over time, at least in my observation.
Copper collectors who use Kraft envelopes often use an inner liner of cotton or some other cloth to isolate the coin from the paper.

Temperature (heat) speeds up the chemical reaction. Envelopes like Kraft etc are usually not archival. You'd want archival/acid-free flips/envelopes for coins you want to keep from damage or toning in the long term.