The two on the top row (phonopost service stamps) are likely due to “changelings.” Therefore they can not be categorized as EFO. Yellow and orange inks are very prone to oxidation and will change to brown after a period of time if not properly stored. 錄音郵件菊色氧化成深棕色.
The middle Chiang Kai-shek $1.70 stamp and the $0.40 stamp may have gone through chemical treatment due to the unusual bright white color on their back side. 蔣像化學劑洗過.
These are just my personal opinions and they may not be accurate.
阿維
2015-06-03 11:19
Thanks I agreed your first one,I am not sure about CKS ,I don't have chemical to try that Did you try that before,if the reason Not light and Chemical,Maybe put wrong words(0.4 and 1.7) when printed
There is a small possibility that the Chiangs' are indeed color error stamp.
For those who are not familiar with the plating of this set, the entire set used one plate except the $1 value (with the denominations changed), all of the sheets can be plated. We know that due to there were studies about the broken "Hwa" variety which is found at position 19/25 on each pane of all values except the $1 value. Therefore only the $1 stamp was printed from a different plate. This provides the possibility for a color error to be made.
That said, I'm not aware of any color error stamp on this set of stamp. If they are indeed color error, there should be a handful of them exist.
As to the light/chemical treatment, yes, I have done plenty of experiments in the past. The most effective one that I found is to apply special chemical agent which is sensitive to certain spectrum light (especially ultra violet), then place the stamp under such light or about one minute, one can change the color or bleach the stamp easily. Depending on which color you want to alter, different chemical agent/light targets different color. This method was first discovered on counterfeit money. In case the color does not match the real money very well, they used this procedure to alter the shade. However, most people can't afford to buy such equipment except those try to print money themselves.
蟑螂
2015-06-04 06:06
Special chemicals can only be attached to the stamp paint it? Because the chemicals will be applied to the entire stamp color. 尤其是這種凹凸版郵票應該不容易吧!
The revenue stamp on the left consists of an error in printing the central vignette upside down. Unfortunately, at some point in time, the original dies of the vignette were obtained by crafty forgers. These forgers took normal examples, chemically removed the central vignette and reprinted the vignette upside down. Some of these examples are still on the marketplace and can fools an unsuspecting collector.
ming8686
2015-06-05 20:20
阿維兄,
小弟與美國的資深郵友正在找這答案 他(老美)也有像您post 的郵票
However, 除了橘色和黃色外 sulfuretting (often misnamed "oxidation", even I use this word sometimes ), a process involving lead that may turn a blue or green stamp to black.
海水或鹽水也會使綠色變深藍甚至黑色 depending on the ink the stamp was used.