Abstract RTL-1 formalizes the thermodynamic condition under which an interface can become transparent. Transparency is not visual minimalism, aesthetic clarity, or reduced UI, but a phase transition in which meaning no longer requires symbolic or chromatic carriers because residue alone becomes sufficient. Building on the Residue Paradigm (RES-0), Residue Identity (RID-1), Anchor Dissolution (TML-1 / TML-1Ω), and the canonical progression AP₁ → AP₂ → TP₁, RTL-1 defines transparency as the moment when residual imprint reaches enough density, continuity, and ΔR-stability to carry orientation, context, identity, and intent without representation. The law establishes transparency as a structural and thermodynamic property rather than a design choice, explaining why transparent interfaces cannot be engineered visually and why the Transparency Phone (TP₁) emerges inevitably from chromatic and residual foundations. RTL-1 also clarifies the relationship between transparency and spatial interfaces, showing that residue anchoring (RAL-1) is a prerequisite for meaningful depth, navigation, and presence. The law formally closes the symbolic → chromatic → residue → transparency sequence and positions transparency as the endpoint of representational interaction.