Ink/Water Stain Vs Donut Vs Tail

Just entering this topic to help young/new stamp collectors understand the difference on stamps they may come across.

I will show....
1 - Water/ink stains
2 - Donuts
3 - Tails

Below are a couple of examples of each to have new collectors recognize the differences.

Below are a couple of examples of water/ink stain caused by droplets of water containing ink mixture and drying out to leave a donut type stain, but is NOT a donut.




Below is an example of a donut...Caused by a foreign object on the plate.



Below is what we used to call a "tail" in the print shop..Caused by ink becoming jelled and flung onto the stamp.



Any other suggestions or additional information for young collectors is appreciated.

Robert