Decide whether to require ASTM C1901 anisotropy (roller-wave/optical retardation) measurement for a heat-treated glass facade

Steps

1. Confirm ASTM C1901's current scope on the ASTM store — a test method for measuring optical retardation in flat architectural glass using polariscope-based instrumentation, used to quantify anisotropy/roller-wave visibility, with retardation reported in nanometers.
2. Determine whether the facade's glazing exposure (large horizontal tempered/heat-strengthened lites, high-visibility low-angle sun conditions) makes anisotropy visually significant enough to warrant a spec requirement — this is a project-specific aesthetic risk decision, not a code mandate.
3. If specifying C1901, define an acceptable maximum retardation value in the project spec, since the standard provides the measurement method but any pass/fail threshold must be established by the design team/owner.
4. Coordinate the fabricator's tempering furnace orientation/process capability with the design team, since roller-wave severity is a furnace/process characteristic, not purely a glass property.
5. Request C1901 measurement data on production or mock-up lites before full production run commitment, since retrofitting anisotropy correction after fabrication is not practical.