Those of us who work on supplying the chemicals know too well about discoloration.

Organics discolor, usually pretty readily, and I am willing to bet that every ink supplied has some additives to minimize discoloration.  BUT, although they may well work MOST of the time, there is no way that an ink manufacturer can totally control the content of his raw materials, and different batches of raw materials will have different levels of impurities and contaminants.  And, be assured it takes only an incredibly tiny amount of a new impurity to foul up the best formulations colors.

Frankly it is a small miracle that you can get consistent, stable colors, given the widely varying chemical and thermal history of the PCB's manufactured.

So, color variation is less surprising, than the lack of it...

Rudy Sedlak
RD Chemical Company... (which does not supply inks!)

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