You can use wet enamel
For this purpose you must fill a small bowl some enamel powder and add some drops of demeniralized (from the supermarket) water.
Always remember that enamel powder and water do not mix like milk in the coffee.
After a short wile the enamel powder will sink to to bottom (it is glass, so its heavier than water).
When applying the wet enamel you have to stirring every time in the wet enamel before getting some wet enamel out of the bowl.

Make wet enamel	Start at the edge
Apply second color	Pickup with the tweezers

Below the sequence of wet enamel (wet pack). 

• Mix the enamel powder with deminiralized water.
• Place the art piece on a paper towel.
• Wen spilling wetpack it will be absorve by the paper towel.
• Pick up with the aid of a flat tooth picker or some other tool a little wetpack out of the bowl and start to cover the art piece.
• Start with the edges..
• Finish the edges and work to the middle of the object.
• Try to work fast as possible and apply the wet enamel on to the copper..
• When everything is covered you can tap with the tweezers to the side of your object.
• It will distribute the enamel even over the surface.
• Pick up your art piece and place it on a firing rack.
• Place the firing rack with your art piece on top of the kiln and let it dry..
• When the powder is dry, it will sparkle and you know it is completely dry.
• Burn it in the kiln.

Wet enamel apple If you want more than 1 color then you must connect the colors on the last moment. This prevent the colors to run trough each other. As an example the apple from the chapter before here on the left. Now it is made only with the wetpack technique. All the colors are applied in one session. The red dots are drops of wet enamel