The answer: nothing really. Serigraph and screen print are synonimous. Silkscreen refers to the same process, but was more appropriate when the mesh employed was actually silk. Now polyester mesh is more commonly used.
But since we are on the subject, how is a serigraph/screen print/silkscreen made? I have never made one myself, so I decided to consult www.essortment.com. Because they provide very thorough, easy-to-understand instructions - far better than any paraphrasing of mine - I will let them take the stage for this post. Here is what they have to say:
"Silkscreen frames can either be handcrafted or purchased in their ready form from any number of retail silkscreen companies. To prepare the silkscreen for printing, it is necessary to prep the screen. Mix one part household bleach to three parts of water and place in a spray bottle. Spray the solution onto both sides of the silkscreen and rinse well with clean water. Allow to dry completely.
Here are two methods of attaching your artwork to the silkscreen. The first is to photograph your artwork and take it to a print shop. Have the print shop create a film positive, which is essentially the opposite of a film negative. A film positive is a clear plastic material with your photographed artwork showing as a black picture of the artwork created. A commercial screen filler is squeegeed onto the prepared silkscreen. Let this screen filler dry completely and thoroughly. Tape the film positive onto the silkscreen and place on an ultraviolet light table. The ultraviolet light will actually burn an image of the artwork through the filler. Wash the silkscreen using a high powered spray hose to remove the filler from the art work area and let it dry completely. Hold your dry screen up to the light and see if there are any light holes showing through the filler (other than the area of your artwork) and tape off with masking tape on the back of the screen. A separate silkscreen must be created for each separate color that is used in your artwork. You should have the print shop break down your photograph into the different colored sections so each section can be burned individually onto a separate screen.
Using drawing fluid, draw your design directly onto the back of the silkscreen. Allow the ink to dry for at least an hour. Pour a thin line of the screen filler just outside of the area of your drawing. Use a thick piece of cardboard for a squeegee and pull the screen filler across the drawing in one fluid motion. It is important that you try to completely cover the inked drawing in one motion as a back and forth pull will erase your drawing. Allow the filler to dry for at least an hour. Rinse the screen with a light pressured water hose to remove the filler from the area of the drawing. Allow the screen to dry completely and then tape off any areas showing light except for the area of the artwork. Create a separate silkscreen for each separate color of your design.
Now that you have your artwork applied to the silkscreen, you are ready to print your first shirt. If you are screening with just one color, you can simply lay your garment onto a flat surface which has been covered with newspaper and lay the silkscreen onto the shirt with the back side of the screen laying against the shirt. Lay down a thin line of paint across the top of the screen and using a rubber squeegee, pull the paint down the screen. The paint will flow through the silk and adhere onto the shirt. This may require two sets of hands, one to hold the screen firmly onto the shirt so it doesn’t move as you squeegee the ink.
For a multiple colored silkscreen design, it will be necessary to secure your silkscreen frame onto a silkscreen machine as the design must be held completely tight and secure to insure that the multi-colored design works properly. Attach each colored screen to the frame and clamp them down tightly. Using a scrap piece of fabric, apply the ink to the individual screens and adjust each screen until the multi-colored design is set in its proper position. After you get a good test piece, you can begin with the shirt. Apply the paint beginning with the lightest shade and work to the darkest shade. After applying the ink to the shirt, it must be set by applying heat to permanently bond the ink onto the fabric."
--Sarah Kramer, Studio Arts Intern