Each icon consists of several main parts. Mandatory are: the carrier and colored layer. Except these layers, the icon can have the substrate, gilding, various insulating layers and a protective layer of lacquer.
The carrier is used to provide mechanical strength of icon. If substrate is not applied, carrier has the role of substrate. The most used carrier is paper, canvas or wooden board.
The substrate is applied to the carrier to provide appropriate color application. Wooden board does not absorb the color evenly. Substrate, which is applied to the board, provides evenly absorption, whiteness and an ideal flat surface. It applies in several layers.
Insulating layers are used to physically separate two layers, to saturate previous layers and reduce their absorption, or to enable easier connection for other layers. For example: before applying Gesso, wood must be soaked with skin glue to be enough saturated, not to absorb skin glue from Gesso. Another example: substrate need to be isolated - saturated with shellac before applying adhesive for gold (substrate does not absorb adhesive if it is well saturated with shellac).
Gilding applies to the icon, which has symbolic meaning: gilding is not often used in secular paintings!
Next to the carrier, colored layer is important and infalliable part of each icon. Technique of painting icons requires applying more thin layers (a new layer applied to previously dried layer).
Function of protective layer is to protect icon with lacquer. After years of icon dirt deposition, cleaning – restoration is much easier when icon is coated with lacquer.