The old fashioned medium for painting on porcelain (and enamel) is a concentration of turpentine of more or less fluidity, called Fat Oil or Essence Grasse. This can be mixed with other oils to change its properties, fluidity and drying time.
MX 54 is a mixture of an acrylic binder and pine oil.
Both are drying mediums and will dry out in your brushes unless you clean them after use with, for example, orange oil.
Water based medium can be washed off the brushes with soapy water.
Fat oil/essence grasse is a derivate of turpentine and as such, should only be used in ventilated locations and inhalation of the fumes should be avoided. Avoid contact with skin, if contact occurs wash thoroughly with soapy water.