Unidirectional Opacity Watermark

A method of forming a laminar assembly, the method comprising:

• forming a plurality of through-holes in a first optically opaque layer;
• positioning an optically transparent core layer between the first optically opaque layer and a second optically opaque layer to yield a stack of layers;
• and
• heating the stack of layers to fuse the optically transparent core layer between the first optically opaque layer and the second optically opaque layer, thereby yielding a fused assembly,
• wherein some of the through-holes are at least partially filled with material from the optically transparent inner layer, and light is visibly transmitted in a single direction through the plurality of through-holes.

A method of authenticating a laminar assembly, the method comprising:

• directing light toward a first side of the laminar assembly and visually inspecting a second side of the laminar assembly for a change in opacity of a portion of the second side of the laminar assembly;
• and
• directing light toward the second side of the laminar assembly and visually inspecting the first side of the laminar assembly for a change in opacity of a portion of the first side of the laminar assembly,
• wherein the second side of the laminar assembly is opposite the first side of the laminar assembly, and
• wherein a visibly detectable change in opacity of a portion of the first side of the laminar assembly or a portion of the second side of the laminar assembly, but not both, verifies authenticity of the laminar assembly.