The best voltage for lining can vary depending on whether you're using a rotary or coil tattoo machine and the type of needle. For coil machines, the voltage range is between 7.5 to 10 volts, while for rotary machines, the voltage range is between 4 to 8 volts. It's worth noting here that even the model of the tattoo machine will affect what level of voltages will be suitable to make it good contouring. So, it's important to note that the voltage setting will depend on the artist's personal preference and the type of tattooing they plan to do. For beginners, it's recommended to start with a lower voltage of around 6 volts until they feel comfortable with a quicker hand speed.
Using too high a voltage can cause the machine to feel too aggressive and reduce control over fine lines. With some machines, too low a voltage under 6 volts can cause stalling, inconsistent power, or excessive needle vibration.
Adjust your power supply's voltage gradually as you get a feel for the machine's response. This will help you dial in the optimal voltage. If working on thicker skin, you may need to go slightly higher on voltage to drive the needle sufficiently deep. Consider using lower voltages around 5-6 volts for delicate tattoo areas like fingers, palms, or faces.