I was curious with pinched harmonics how can you get them to sustain longer? for some reason, i can only get them to sustain for a few seconds at most. I do run my amp at a low volume seeing i cant be too loud with it. Could it be that? Perhaps im just doing something wrong. i guess a good example of what im going for is something like Glen tipton tends to do with priest. He can just magically throw in harmonics not only on their own but on top of a note already played (havent quite figured that one out) and his sustain on them is crazy.

Gibson Les Paul
Danelectro DC-59
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Volume is a huge thing. Also gain. Good cables. Changes strings. etc
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some harmonics sustain longer than others, in pinch-harmonics the sustain can be different depending on where you do the pinch. exactly in the middle between the fret you're holding down and the tremolo will always have the best sustain. The guitar is relevant to, this part is just like normal sustain; it depends on how you neck is built etc.
Gain is definately a huge part of it. Also, if you throw in a bit more treble (but still balance your tone well) you can get more sustain on pinched harmonics.
I seem to get the best sustain when i'm using a lot of distortion and whatnot.
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You really should just play around with everything including volume, gain and distortion, tone and anything else and just test it until you find something that works for you. But for me it seems the gain works the best in past experience.