# Σε τι διαφέρουν οι νερομπογιές από τα χρώματα της νωπογραφίας;



## nickel (Sep 13, 2013)

Οι μπογιές που χρησιμοποιεί ο ζωγράφος που ζωγραφίζει ακουαρέλες (υδατογραφίες) πάνω σε χαρτί σε τι διαφέρουν από τα χρώματα που χρησιμοποιεί ο ζωγράφος νωπογραφιών (frescoes) που ζωγραφίζει στον τοίχο;


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## daeman (Sep 13, 2013)

...
Ως χημικός που αυτά τα θέματα δεν τα ξεπετάει στα γρήγορα, επιφανειακά και αβασάνιστα, σύντομη απάντηση δεν έχω, ορίστε όμως υλικό για διάβασμα:

_*Fresco*_ (plural frescos or frescoes) is a technique of mural painting executed upon freshly laid lime plaster. Water is used as the vehicle for the pigment and, with the setting of the plaster, the painting becomes an integral part of the wall. The word fresco (Italian: _affresco_) is derived from the Italian adjective _fresco_ meaning "fresh". Fresco may thus be contrasted with _secco _mural painting techniques, on plasters of lime, earth, or gypsum, or applied to supplement painting in fresco.

_Buon fresco_ pigment mixed with water on a thin layer of wet, fresh plaster plaster, for which the Italian word for plaster, _intonaco_, is used. Because of the chemical makeup of the plaster, a binder is not required, as the pigment mixed solely with the water will sink into the _intonaco_, which itself becomes the medium holding the pigment. The pigment is absorbed by the wet plaster; after a number of hours, the plaster dries and reacts with the air.

_A secco_ painting, in contrast, is done on dry plaster (_secco _is "dry" in Italian). The pigments thus require a binding medium, such as egg (tempera), glue or oil to attach the pigment to the wall. It is important to distinguish between _a secco_ work done on top of _buon fresco,_ which according to most authorities was in fact standard from the Middle Ages onwards, and work done entirely _a secco_ on a blank wall. Generally, _buon fresco_ works are more durable than any _a secco_ work added on top of them, because _a secco_ work lasts better with a roughened plaster surface, whilst true fresco should have a smooth one. The additional _a secco_ work would be done to make changes, and sometimes to add small details, but also because not all colours can be achieved in true fresco, because only some pigments work chemically in the very alkaline environment of fresh lime-based plaster.
http://en.wikipedia.org/wiki/Fresco#Technology

*The Art of Fresco: Color*

Watercolor paint consists of four principal ingredients:


*pigments*, natural or synthetic, mineral or organic;
gum arabic as a *binder* to hold the pigment in suspension and fix the pigment to the painting surface;
*additives* like glycerin, ox gall, honey, preservatives: to alter the viscosity, hiding, durability or color of the pigment and vehicle mixture; and
*solvent*, the substance used to thin or dilute the paint for application and that evaporates when the paint hardens or dries.


*The Stuff of Paint*
*Watercolor: What it is.*







_Gum Arabic Crystals_Traditional transparent watercolor is finely ground pigment in a water-soluble binder such as *gum arabic*. Gum arabic is water-soluble gum produced by a species of the acacia tree and is available in crystalline form or in prepared solutions. The gum arabic crystals or granules are transparent when pure, but less highly refined varieties can be yellowish to honey colored. Gum arabic is also used in inks, adhesives, pharmaceuticals, and confections (it's non-toxic and tasteless).


Other binders used for watercolor paint have included *Tragacanth*, a gum optained from various asian shrubs, and *fish glue*. *Glycerine*, *dextrin*, *crystallized sugar*, *syrup*, or *honey* can be added to modify the working texture of the paint, counteracting the brittle quality of the gum arabic a bit. *Ox gall* can be added as a surfecant or wetting agent to aid the free flow of washes. (Think dishwasher soap's "sheeting action") *Oil of cloves* can be added to deter the growth of molds which can happen on cheap quality paints.
 

Been there, done that, ecce homo to prove it. :devil:


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## nickel (Sep 13, 2013)

Served on a platter. I like. (So does Salome.)


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