Za edna grupa sivi sădove ot Jugoiztočna Bălgarija : Kăm văprosam za pojavata na sivite amfori v Trakija (kr. VII-VI v. pr. X.). On a group of grey vessels from South-eastern Bulgaria and the problem of the adoption of the grey pottery in Thrace (end of 7th - 6th c. BC). - Nikov, Krassimir (Bălgarska Akademija na Naukite, Sofija, 2005)