Abstract Bent copper tubes have been successfully used for solid state reactions at high temperature, under nonoxidizing atmosphere. They provide an inexpensive and convenient alternative to gold and platinum for reactions between fluorides, and do not reduce some elements such as tin(II), as nickel does. Solid state NMR studies of fast fluoride ion conductors Pb 1− x Sn x F 2 prepared in copper tubes show that contamination by paramagnetic Cu 2+ is minimal. 119Sn Mössbauer spectroscopy is used as a sensitive probe for the formation of SnO 2, and indicates that no oxygen leaked in the tubes. Like any reaction carried out in a sealed container, those resulting in a gas being evolved and/or highly exothermic reactions can lead to explosions and thus must be avoided. An attempt to synthesize TiI 4 in a sealed copper tube is described, as an example of a dangerous uncontrollable reaction by this method.