Etching / Cleaning / Decapping is a chemical operation that removes the surface layers of a material using acids or alkalis. For metallic materials, decapping removes the surface layer of oxides or other impurities to make the metal surface suitable for enamel coating.
The decapping process has a specific duration, which depends on the volume and dimensions of the container.
Once the decapping process is complete, all components are visually inspected to check the effectiveness of the process.

The following are examples of boilers whose decapping process has to be carried out or repeated due to rust residues on the surface of the sheet metal.

In contrast, the following are examples of boilers that have been successfully decapped.


After deacidification / decapping, the inner surface of the workpiece takes on a porous appearance, allowing the glaze to bond firmly to the substrate.

Before applying the glaze, the following should be carried out:

  • closing/filling of the lateral supports;
  • closing of the rim (180, 290, 480) with the appropriate dimension.

The main purpose of glazing is to ‘protect’ the piece and to give it an attractive and glossy appearance after application.


Drying of boilers to be enamelled is only carried out when the enamels have been applied in liquid form.

The purpose of the drying process is to remove the make-up water from the moulded pieces in a carefully controlled manner to ensure the integrity and regularity of the piece’s shape and size.

Water removal takes place in two distinct stages:

the process of liquid water diffusion inside the boiler, through which it reaches the surface of the component,
the process of evaporation of water from the surface of the component itself.


In order for the enamel applied as a dry or dried layer to adhere well to the substrate, heating to a high temperature for a suitable period of time is required. This heat treatment, the final operation of the entire glazing process, is called firing or vitrification.

The vessels, after undergoing various surface treatment operations and applications in different systems, are introduced into the furnace to melt and then vitrify the enamel.