I am trying to measure the amounts of voltages that I can get out of dry bones due to their piezoelectric properties. (basically I place the bones in between two copper metal plates with wires taped to the top and bottom of the plates). The problems I encountered was that even without releasing much stresses onto the metal plate i can still get a voltages reading and that number just stay there without me doing anything. And when my hands kind of touches it again, the voltages increased. I went to ask someone and they told me that it might be the static electricity that were built on my hand and that I should touch a metal material before doing the experiment. I did, and the same thing still happen, even after multiple tries. Just what am I doing wrong?? (I also tried putting book in the middle of the metal plates instead,and I was still able to get voltages reading).

How high is the voltage?

it's not that much...around .1 volts

If the voltages you are getting are sinusoidal and mains frequency they would be pick up from nearby wiring. You would need a cathode ray oscilloscope to see the waveform shape and determine its frequency.

This bit

"I also tried putting book in the middle of the metal plates instead,and I was still able to get voltages reading"

is interesting.

What sort of voltmeter are you using?

Is it one with a very high input impedance (an electrometer)?