**2.6 Electric and magnetic field**

The principle of the method benefiting from electric fields relies on the separation of the nucleation and crystal growth; it can be applied in the electric as well as the electromagnetic field. The nucleation process takes place while the current is switched off [28]. In order to perform crystallization experiments in the electric field, the specially designed crystal growth cell has to be used. The system contains two parallel electrodes and is connected to a direct current source that provides direct or alternating current. Nevertheless, the experiment has to be set up before the application of the current. It was reported that the current positively influences the size of protein crystals. Specifically, lower frequencies of alternating current provide less larger crystals compared to higher frequencies [28]. For the purposes of using electric current the e-crystallization cells based on vapour diffusion or batch method were made [29].

In the case of using magnetic fields, there is a similar outcome as carrying out an experiment in microgravity. This can be achieved when using a vertical magnetic field with use of anti-gravitational force. The crystals treated by magnetic fields show better diffraction quality as was revealed for microgravity experiments [30, 31]. In addition, the crystallization conditions need to be known before initiating the experiment. Moreno 2017 mentions the use of gels for obtaining large well-arranged crystals together with use of magnetic forces for at best two days and more days. For this type of experiment, the capillary glass pipettes were reported to be suitable for use of homogeneous or nonhomogeneous magnetic fields [28]. The best influence of magnetic field use is regulation of quality and crystal size [32].
