[innerlight]

Any reflective surface could be used for scrying. Whether it's a bowl of water/oil, marbles, or crystals, modified mirrors. Colored glass may even make it easier to scry with than clear.

Since you have acquired this from someplace, saging and cleansing it would be a must. Clearing out any prior energies that were used for this item in the past. Like Lynn said it would not hurt to ask it its permission to do so. I would also set ones intention of making this a scrying item, and keep that as it's specific and only purpose. Don't go using this for other uses. Don't mix energies like that.

Tips for scrying with it, once all that is done. Would be, to really get into your normal routing for relaxing. Dim down your lights, and perhaps get a soft light to give you some ambience. And then just gaze at it. It may help to gaze indirectly at it. You could also put a candle behind it, and allow it to light it up that way, and see if anything comes through that way.