I know some people will freak out with what I'm going to say and cry "heretic", but it needs to be said.
All these ideas that the way that the icon is painted (technique) portrays holiness/theosis/wisdom/ ascesis etc appeared in the twentieth century and have absolutely nothing to do with what the Church Fathers actually teach about icons.
For centuries after the Renaissance and the dominance of naturalistic painting the Byzantine icon (and anything Orthodox for that matter) was disdained by the artistic and scientific world (including in Orthodox countres). Orthodox iconography was considered to be primitive and crude and painted by uneducated painters who didn't know the basic principles of painting.
At the end of the 19th/beginning of the 20th century a revolution took place in European art. New aesthetic values and new visual forms were introduced as well as the reevaluation of the relationship between the form and the content in a work of art. One of the immediate results of this revolution was the different view of the role of the artist in the act of painting. Whereas previously the artist was compelled to express the content of his work with existing naturalistic forms, he now has a more dominant position in his art work. He is able to control the forms in his work that express the content in a completely personal way. This climate gave birth to various artistic trends, and a great variety of "visual languages" that are distinguashable between them and can be interpreted in various ways.
It was this revolution of Modernism that brought about the reevaluation of the iconography of the Orthodox Church and the peculiar manner in which it is painted. The icon slowly began to be admired by scientists, artists and theologians.Unfortunately this admiration was not based on the right presuppositions and one-sided means of interpretation were developed that emphasised only certain characteristics of the icon and in particular the theological/dogmatic aspect of the icon. The result was that the icon being viewed based on the facts of European art and in contrast to Western/Roman Catholic art, was incoroperated into the same form of art as Modern Art. Researchers/theologians/ philosophers understood the art of making icons and the art of the icon in the same manner as Modern art - that is as the creation of an image using a specific "visual language" that is capable of making visible the high truths of the Orthodox faith and able to suitably present the spiritual state of the persons portrayed.
The main representatives of this school of thought were P. Florenski and L. Ouspensky who introduced the idea that the form of the person portrayed isn't enough for it to constitute an icon (In other words the theology of the Fathers was not enough for them.) For these theologians what makes an icon an icon is the expression of the existential state of the person of Christ and the saints. So if a person is also God (as is Christ who by nature has both divine and human nature) or by grace participates in the divine energy (the saints) then the icon must find a way of portraying this. In other words the focal point of the art is the expression of a reality that is beyond the form and this turns iconography into an expressionistic artform, that aims to express some content with the painted form.
The immediate result of this is that the "visual language" is bound to the Truth and is given a dogmatic dimension. When the technique is that which expresses the transcendent content, then it becomes the very essence of the icon so that without the specific visual language (in this case, byzantine technique) the icon ceases to be an icon, since it does not express the content and does not visualize the holiness/divinity of the person depicted. This inovative teaching was never taught by the Fathers of the Church. This is why today, icons painted in a naturalistic manner, many of which are miraculous, are described as heretical (Though these same people completely ignore that the famous Sinai icon of Christ is painted in a naturalistic manner).
The result of this is that the manner of painting (technique) aquired dogmatic validity to the degree to which it expresses, symbolizes, describes and defines the Truth of the Church, and consequently it cannot change. The result is that the iconographer too assumes the role of the theologian who expresses the truth, not in words, but in form and colour.
I will state again that this idea is found nowhere in the Fathers of the Church and only creates problems and impasses.
One of the first problems created by this dogmatic understanding of the icon and technique is the inability to comprehend the immense variety of forms and manners the Byzantine and post-byzantine iconographers used in order to paint Orthodox icons. A quick view of history shows that in every era iconographers used different techniques to paint icons. In the era immediately following the Iconoclast controversy, when iconographers were incredible careful of the way they painded icons, there is a great variety of technique (including naturalistic) and they often combined more than one technique in an icon. The technique of iconography has history, it is not like the Symbol of Faith, that one it had been stated, it could never change. While there are things in the icon that cannot change (the form of the person/event depicted - that is the Father's definition of the icon), there are other elements (technique) that have altered a great deal: the colour of the background, the general understanding of colour in various schools, proportions, movement etc. In many cases the manner of painting the forms, clothing, space differs drastically from one school to another. If the technique had the dogmatic content that it has been loaded with this would amount to heresy.
The same interpretive problems arise with the use of the same technique for painting saints and sinners. If the technique used portrays the holiness/ theosis of the person depicted, then why is Judas (and other sinners) painted in exactly the same manner as Christ and the saints? Most Western Orthodox Christians would be horrified to know that the Byzantine technique was never used exclusively for painting icons. It was never loaded with the dogmatic content it aquired in the 20th century.
Loading the technique with dogmatic meaning leads to inability to comprehend the history of iconography. and if we don't undertand the history of iconography we aren't going to make much sense of the present.
At the moment I don't have time to go into all the theological problems that arise from this misinterpretation of icons. In trying to find a place in the modern world for icons, the Russian theologians of the 20th century almost completely ignored the already existing theology of the icons of the Holy Fathers and the 7th Ecumenical Council and created their own completely new definition of the icon based on the definitions of Modern art. That is hardly scientific methodology.
For the Holy Fathers, the icon is the bodily form of the person depicted, nothing more. Nowhere do the Fathers talk about symbolism of colours, proportions or any such nonsense. (Symbolism was banned by the Quinisext council). The Fathers are completely realistic and historical. If the person was old their face has lines.
If I speak in the tongues of men and of angels, but have not love, I am only a resounding gong or a clanging cymbal. 
