The diagnosis and the study of the properties of quark–gluon plasma can be undertaken using quarks not present in matter seen around us. The experimental and theoretical work relies on the idea of strangeness enhancement. This was the first observable of quark–gluon plasma proposed in 1980 by Johann Rafelski and Rolf Hagedorn. Unlike the up and down quarks, strange quarks are not brought into the reaction by the colliding nuclei. Therefore, any strange quarks or antiquarks observed in experiments have been "freshly" made from the kinetic energy of colliding nuclei, with gluons being the catalyst. Conveniently, the mass of strange quarks and antiquarks is equivalent to the temperature or energy at which protons, neutrons and other hadrons dissolve into quarks. This means that the abundance of strange quarks is sensitive to the conditions, structure and dynamics of the deconfined matter phase, and if their number is large it can be assumed that deconfinement conditions were reached. An even stronger signature of strangeness enhancement is the highly enhanced production of strange antibaryons. An early comprehensive review of strangeness as a signature of QGP was presented by Koch, Müller and Rafelski, which was recently updated. The abundance of produced strange anti-baryons, and in particular anti-omega Ω Ω ¯ ¯ ( s ¯ ¯ s ¯ ¯ s ¯ ¯ ) , allowed to distinguish fully deconfined large QGP domain from transient collective quark models such as the color rope model proposed by Biró, Nielsen and Knoll. The relative abundance of ϕ ϕ ( s s ¯ ¯ ) / Ξ Ξ ¯ ¯ ( q ¯ ¯ s ¯ ¯ s ¯ ¯ ) resolves questions raised by the canonical model of strangeness enhancement.