tempering glass spacer

The invention relates to an object comprising at least a glass spacer between a first element of said object and a second element of said object, said spacer comprising an alkali metal ion concentration gradient from the surface and perpendicular to its surface. The object may be a solar collector in vacuo. The invention also relates to a glass bead having a gradient of concentration in alkaline ion from its surface and perpendicular to its surface and its use as a spacer supporting a pressing force between two elements, said pressure pushing the two elements towards each other.