SnO2 has been used as pigment in the manufacture of glasses, enamels and ceramic glazes. Pure SnO2 gives a milky white colour; other colours are achieved when mixed with other metallic oxides e.g. V2O5 yellow; Cr2O3 pink; and Sb2O5 grey blue. Tin(IV) oxide can be used as a polishing powder, sometimes in mixtures also with lead oxide, for polishing glass, jewelry, marble and silver. Tin(IV) oxide for this use is sometimes called as "putty powder" or "jeweler's putty". SnO2 coatings can be applied using chemical vapor deposition, vapour deposition techniques that employ SnCl4 or organotin trihalides e.g. butyltin trichloride as the volatile agent. This technique is used to coat glass bottles with a thin (<0.1 μm) layer of SnO2, which helps to adhere a subsequent, protective polymer coating such as polyethylene to the glass. Thicker layers doped with Sb or F ions are electrically conducting and used in electroluminescent devices and photovoltaics. SnO2 is used in sensors of combustible gases including carbon monoxide detectors. In these the sensor area is heated to a constant temperature (few hundred °C) and in the presence of a combustible gas the electrical resistivity drops. Doping with various compounds has been investigated (e.g. with CuO). Doping with cobalt and manganese, gives a material that can be used in e.g. high voltage varistors. Tin(IV) oxide can be doped with the oxides of iron or manganese.   1990 NFL season  The 1990 NFL season was the 71st regular season of the National Football League. To increase revenue, the league, for the first time since , reinstated bye weeks, so that all NFL teams would play their 16-game schedule over a 17-week period. Furthermore, the playoff format was expanded from 10 teams to 12 teams by adding another wild card from each conference, thus adding two more contests to the postseason schedule; this format remained in use until 2019 (there were four division spots and two wild card spots available with realignment in 2002). During four out of the five previous seasons, at least one team with a 10–6 record missed the playoffs, including the 11–5 Denver Broncos in 1985; meanwhile, the 10–6 San Francisco 49ers won Super Bowl XXIII, leading for calls to expand the playoff format to ensure that 10–6 teams could compete for a Super Bowl win.