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A spot plate, also called reaction plate, is a laboratory tool used for qualitative determination of reagents.
Spot plates are commonly made of glazed porcelain, though sometimes glass and plastic spot plates are also available. Spot plates consist of a flat plate with several potholes (also called cavities or wells), usually 6, 12 or 24. Glass and plastic spot plates are sometimes referred to as staining plates and are often used in cell culture.
Inside these potholes, a drop of reagent is added, and a drop of another reagent is added to observe any reaction that might (not) appear. For multiple reactions, add a drop of reagent in each well.
Spot plates are sold by chemical suppliers. They can also be bought online.
If you don't want to buy a spot plate, you can use an egg platter instead.
Dentistry suppliers also sell this item, under the name mixing plate.
DIY spot plate
A simple spot plate can be made by heating a rounded metal item like a ball using a heat gun, then pressing the heated metal against a thick flat plastic sheet until a pothole is created. Be warned that this method may not work well on all plastics, some may char, while others may not be compatible with organic solvents. This procedure does not work on glass, as it may crack or deform differently.
Another way is to make a plate out of gypsum or cement, create a few potholes using a metal ball, and then let the gypsum dry. Coat the part with potholes in a chemically resistant coating, like hydrophobic paint or silicone, to obtain an inert surface.
To make a real spot plate, you must first make a plate out of wet clay, then make a few potholes in the plate. Let the clay dry completely, then fire it in a kiln. Coat the plate in chemically resistant glazing, dry it, then fire the glazed plate to finish it. Inspect the spot plate for any defects.
Mixing palettes used in painting are a suitable alternative to spot plates, provided you don't use very corrosive reagents.