Regummed? How Do You Know?

Can someone tell me how to distinguish between old stamps with their original gum and those that have been regummed? I may have stamps that I always assumed had their OG, but never knew the difference. Please post pictures if you can. Thanks.

Regummed will normally show gum at the edge of the paper and inside the perforation holes, will need good magnification to detect it. Most stamps were gummed before being perforated, and hence will not have gum at the edges.
Additionally the color/appearance of regummed will often be different from original gum, don't have any images available right now.

This will give you a start:

https://www.hgitner.com/regummed-stamps.html

Familiarity with the right gum for the right issue will also help.

Gum on perf tip fibers. Crackled gum.

The old giveaways were things like gum caught in the perf tooth fibers, gum bleeding onto the front of the stamp, gum of uneven thickness or incorrect texture, or gum that's the wrong color/type for the issue.

Unfortunately, modern sophisticated regum jobs have none of those "tells". The gum used is authentic gum taken from another, cheaper stamp of the same period and country. The gum is applied to the back evenly with the perf fibers embedded in a substance (like soft clay) which prevents the gum from leaching to the front or getting caught in the fibers at the tip of the perf teeth. The gum is applied using a brush or roller in a manner that is correct for the issue, so the gum will have the right texture. That was the state-of-the-art about 20 years ago, I'm sure they have other tricks as well by now to help them escape detection. Regums done this way can be very deceptive, and accordingly often come with certs saying "full original gum MNH", or expertiser's marks on the back for countries like Germany that value such marks on the back.

Don't trust gum.

EDIT to add: This is one of the cases where an old certificate is better than a new certificate. If your classic MNH stamp has a 1975 cert saying "full original gum", you can be more confident (not totally confident, but more confident) that it's not a modern regum job.

Today gum is often air brushed on and if well done can be deceiving. (In the past, a good regummer would 'pot' the stamp in clay and protect the perfs.) On some stamps the 'curl' test can be used, place the stamp face down in the palm of your hand and allow your body temperature to heat the stamp. If the stamp has been regummed, the stamp will often curl. I assume it curls do to the uneven temperature changes with any additional gum layers that have been applied.
Obviously this is a not a fool-proof method, but can sometimes give you another piece of info for a decision.
Don

it is a mismatch in stress (either expansion on heating or shrinking on cooing) between the gum and the paper

thanks

maybe off topic, not sure, but - how to tell if a stamp is ungummed or had it removed?

An excellent question Stamps4Life.

A quick look in your catalogue will tell you if a particular stamp was issued without gum.

I do see in the front of the Scott cat I have for 2019, Germany, they use an (#10025;) to denote no gum. But when I look in the catalogue, for instance for Scott C2 AP2, they do not use the (#10025;) but just say ungummed. I was wondering where the (#10025;) is used????

There is no easy way to tell regumming. Experience is everything, I believe. The best way to learn would be to acquire several of the cheapest hinged mint stamps of the same set (if that is possible) that are also badly centered, being the least likely candidates for regumming. Faulty with gum would be just fine. Then compare finish, thickness, appearance on or around the perfs, everything except maybe color as gum often ages more readily than paper.

Sorry, but some of best US regum jobs date back to the 1970s, maybe earlier, not done by any of the methods mentioned.

Also, the curl test is unreliable in the case of a change to high humidity where many stamps will curl and even roll up. This seems to apply to stamps that were probably stored for their entire lives in very low to moderate humidity (less than 40-50%) and are brought out into something like 90% humidity weather.

I'm sorry Stamps4Life, I don't know what the #10025 means.

I did look at my 2014 Classic Specialised and it states that Germany C2a is ungummed but not C2.

Sorry for the confusion - Apple star icon was converted to #1025..... Scott catalogue uses (star) when referencing ungummed. But I don't see the (star) in the example I listed and was wondering where they use that reference in the catalogue. I do see the word ungummed so it's a moot point I guess. But I'm trying to learn the catalogue and wanted to make sure I'm not missing the " (star) " somewhere.

Another lesson learned - no using Apple imoji's.

FYI - others know this im sure, but I didnt. The chart in the front of the catalogue makes note of stamp conditions. I assumed, I know, and was expecting to see the symbols therein used in the catalogue. Scott doesnt use them. Scott refers to them as "commonly used symbols" not necessarily used in the catalogue. Scott actually lists as ungummed. Tks bobby de la rue for helping me figure it out. have a nice day.