You must learn how to ensure a piece of artwork is not a fake reproduction to preserve your investment. Unfortunately, many works of art are forgeries that charlatans sell for a profit. Even with the help of highly trained scholars to identify reproductions, forgeries are still able to make it into the mainstream market.
Use a magnifying glass to decipher if a pattern matrix exists behind the oil. Reproductions will typically use a dot matrix that fakers then cover over with egg yoke to create the illusion that it is a real oil painting.
Observe the material the art is painted on. Forgers usually paint knock-offs on inferior forms of canvas, cardboard, fiberboard, poster board and paper. For original oil paintings, the artists used thick canvas, Masonite panel or wood.
Hold the painting at an angle and up to a light source, so you can see the reflection of light on the surface. A reproduction will have a completely even surface and consistent texture. Original paintings have brushstrokes that end at the edge of the colour, then continue through many colours. In an original, you may also find hair particles from brushes that have completely dried into the paint.
Flip the painting over and look for copyright information. Original paintings will not contain any copyright information.
Check the edges of the painting if it is on canvas. An original oil painting will have a rough and uneven paint edge on the sides. If the side is even, then it is probably a reproduction.
A quick method to test the validity of an oil painting is to prick it with a pin. Observe the residue that is left on the pin. Oil paints take decades and even centuries to completely dry out depending on the paint.