Needles should be inspected with a magnifying glass or jewelers loupe prior to use. Each needle of the needle group soldered to the needle bar should be sharp, straight, and parallel. Examine the group from multiple angles to ensure that no single needle is sticking out of line or is not parallel to the group. Discard any needle bar with needles that are bent, dull, or out of alignment. Never use a needle bar more than once, even on the same client.
The most common needle shapes used for shading and coloring are four and six needle straight shaders. The needle groups are soldered straight across on the needle bar in a line. The needle tubes that hold the needle bar have a straight, flat hole that closely fits the group of needles. Needle tubes are interchangeable and come in many shapes and sizes to accommodate different sized and shaped needle groups. Tubes also differ in size and weight, to accommodate the preferences of the artist.
The tattoo needles must penetrate deeper for shading and protrude further from the end of the needle tube than when they are set for line work. The contact screw at the top of the tattoo machine is adjustable to change the size of the gap between the contact screw and the armature bar, which vibrates up and down to move the needle bar. The correct gap setting for shading is 2 mm, or approximately the thickness of a United States nickel.
Set the tattoo machine speed for shading. Some models of tattoo machine display a voltage readout, which can be useful for setting the speed correctly. For shading the voltage should be 4 volts or less. The majority of tattoo artists adjust voltage by listening carefully to the sound of the machine; it should produce a steady buzz or a hum. The sound of the machine should not crackle or make a staccato noise, like a typewriter or a machine gun.