Cake decorators regard Stringwork as "the Rolls Royce of cake decorating." It is an extremely delicate form of cake decoration, also known as extension work. Stringwork is draped on the cake before applying borders. It is also used when writing on cakes. 

Different types of decorations and inscriptions are made by the following two methods used for delicate Stringwork: the Falling Method and the Contact Method. This type of work is best done with a parchment cone, because you have more control, but it can be done with a pastry bag, as well. 

Designs are usually made directly on top or sides of a frosted cake. You can also trace a design onto it and then pipe the lines with icing. My favorite is to use a Designer Pattern Press which imprints elegant designs for easy overpiping. 

The position in which the cone or bag is held must be held in a certain angle, or the position relative to the work table and direction  to produce a specific design.

In general, hold the top end of the cone between the thumb and the first two fingers of the right hand. Steady, even pressure at the top of the parchment cone makes an even line without breaks. The fingers should be positioned so that the the thumb is locked over the closed end with the remaining fingers curled around the side, fairly perpendicular to the surface to be decorated -- hold a pencil in your hand; it is held pretty much the same way. Lightly hold the index finder of the left hand against the thumb of the right hand or against the cone in order to steady your right hand and help guide it.

With the right fingers, apply an even, medium pressure to squeeze the icing from the cone, otherwise you get lumpy lines. Control the thickness of the line by adjusting the pressure of your thumb; squeezing harder makes a thicker line. Move with flowing and even movements to prevent the line from breaking. Slow down the flow when making circles or curves; the contents will curve and loop automatically. 

The Falling Method (Exaples): The falling method is so called because the cone is held above the surface, and the icing is allowed to fall or drop from the tip of the cone onto the surface being decorated. Usually the method for applying strings is to 'touch to start and touch to end.' Let the string drape freely as you move to your right (if you are right-handed). This method allows you to make very fine, delicate lines and patterns while keeping the thickness of the line perfectly even. Much, if not most, parchment cone work is done this way, generally with royal icing, melted chocolate, or piping buttercream. 

The opening in the tip of the cone should be cut quite small. At first, it may seem difficult to control the line while holding the cone an inch above the surface, but with practice you will be able to make very precise patterns.

To pipe with the Falling Method, hold the parchment cone vertically. Touch the tip of the cone to the surface attach the icing to the point where you want the line to start. Then, as you begin to squeeze the cone, lift the tip of the cone from the surface and start the line. Hold the cone about an inch from the surface as you trace your pattern. The thread of  icing is suspended in the air between the tip of the cone and the surface being decorated. Keep the pressure light and constant. To finish a line, lower the tip of the cone and touch the surface at the point where you want the line to end. At the same time, stop squeezing the cone. 

The Contact Method (Examples): The contact method is used in two cases: (1) When you want to vary the thickness of the line; (2) When you want to decorate a vertical surface, such as the side of a cake. Hold the cone as you would hold a pen, with the tip in contact with the surface and at an angle of about 30 to 45 degrees. Draw lines as though you were drawing on paper with a pen. Control the thickness of the line by adjusting the pressure of your thumb. Squeezing harder makes a thicker line. 

It takes a fair amount of practice to control the thickness of the line. Normally, it is best to practice the falling method first, until you make simple lines and patterns easily. Then, when you practice the contact method, you can concentrate on controlling pressure.  In addition to royal icing, fondant, and chocolate, buttercream  is also used for decorating with the contact method. methods from pastrywiz.com

More Stringwork Tips: .

Icing should never be really stiff for strings. If it is, the stringwork doesn't stick as well and when you move the cake the strings fall off. (Add more liquid if you are having this problem).

Usually strings are applied with a #3 tip. Larger and they look too heavy and smaller are very fragile. This is not a 'rule' but what I usually do. (Cornelli lace should never be applied with anything larger than a tip 2.) And I have seen other cakes that the tip 3 do not apply to also. 

Practice! Practice on small cakes that don't matter so much, then do the strings on wedding cakes.

Do strings in WHITE on WHITE at first. If you make mistakes, pulling them off won't show. 6. DO NOT fill the bag too full. You will have much better control. I like 10" bags for this too.

Cakes with stringwork should always be placed on sturdy boards (or separator plates) that won't'give.'

If while learning, you plan to apply stringwork OVER GARLANDS, it is easier. With Stringwork applied directly to the iced cake (just strings, no garlands,) you'll have much more breakage. 

The illustrations below show simple patterns made with either a pastry bag or a parchment cone, called the Falling Method. This is the method that the beginner should practice and master before proceeding to more complicated designs. Any of these designs can be practiced by first drawing it in dark ink on a sheet of paper, then placing a sheet of translucent parchment or a plate of glass over the design. Pipe the icing onto the parchment or waxed paper, using the design underneath as a guide.  

All lines need to be equally thick and all loops of equal length, depth, height and size.

All lines need to be equally thick and all loops of equal length, depth, height and size. Don't loose your cool. You can make it.

First pipe and then pipe the same pattern the opposite way on top.

This one is also a combination of 2 decorations piped on top of each other.

This one is pretty cool. It requires a restart as it is not piped in a continuous line like the other ones are.

Make sure you apply constant pressure on the cone so that all the lines are equally thick. Try to pipe straight lines (not easy I know!) and keep the space between the lines constant.

All lines need to be equally thick Keep the spacing between the lines constant in every direction so that the squares have sides of equal length.

Here again, keep the spacing between the lines constant so that all lines are of the same length, resulting in an unfinished square.

All lines need to be equally thick and all waves of equal length, depth and height.

This is the same as above, but with a second wave line piped on top in the same, but upside down matter.

This is mostly used for petit fours or rectangular cakes. Pipe 2 triangles and one loop on top of each other.

Pipe 3 times the same pattern using different length on top of each other.

The musical note uses a touch of the the contact method. Start from the inside out and make sure you end in a dot (not a Hershey's Kisses)

A simple swan, start playing with your piping thickness for more contrast.

The illustrations below show more sophisticated patterns made with the Contact Method.  Beginners should first practice the falling method before proceeding to more complicated designs. The contact method is used when you want to vary the thickness of the lines. 

Hold the cone as you would hold a pen, with the tip in contact with the surface and at an angle of about 30 to 45 degrees. Draw lines as though you were drawing on paper with a pen. Control the thickness of the line by adjusting the pressure of your thumb. Squeezing harder makes a thicker line.

TRACED DESIGN: Pipe strings over a traced design. To make a pattern:

1. Cut a long strip of parchment paper, sized to fit around the perimeter of the cake, and about 1/2 way up the height. Fold the paper several times until it is approximately 2 inches long, then cut parallel curved links off two opposing corners.

2. Open the paper to reveal a scalloped design. Place it around the cake and trace the design onto the cake with a toothpick.

Positions:
- Bag: slightly less than 90° angle
- Tip: close enough to cake so that icing attaches without scraping cake with tip and without flattening icing strings.

Sequence:
1. Starting at one edge of the traced design, pipe an icing string line.
2. Move tip up, around and down to produce different effects.  
3. Do not let lines touch or cross.
4. Let dry before adding other icing trims.

Some information and a few pictures from www.wilton.com.