OOOOOOOOOOOOOO Rafa where does one start. There are so many variables. Basically Tabriz is a city weave and you are looking for good even weave and good symmetry. The finer it is the sharper the outlines should be. Unfortunately in the past 25 years the production in Tabriz has been polluted by using bad dyes and artificial silk (Rayon) instead of silk. While there are good productions as well but one has to be very careful. In any event my personal taste in Tabriz is old pieces, which have a very wonderful weave (not necessarily extremely fine) and lovely handspun wool with natural dyes.
I could go on for a few pages but I hope the above is of some help.
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