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All responders have given good instructions. Let me add that the emulsion, or dull side, of glass plates is often very fragile. They may also toxic from residual bromides, iodines, and mecury. Handle them only by the edges preferably with either lintless cotton gloves or the latex variety as found in a doctors office (I prefer the later).
Think twice about using an enlarger for other than a light source for contact printing. Conventional condensor enlarges with tungsten or quartz lamps will probably crack the glass because of the heat generated. If you must englarge, consider a cold head enlarger, essentially flourescent.
What is the vintage of these glass plates. What is the subject matter? Are they civil war, victorian, or old french nudies. I'm not snooping but suggesting that the answers also may determine how to best accomplish your purpose.