What section thickness is recommended for Congo Red staining of amyloid?

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Staining quality for Congo Red–amyloid relies on having a section thick enough to allow uniform dye penetration and to preserve the ordered structure that gives Apple-green birefringence under polarized light. The recommended thickness of 8–10 microns balances these needs: it’s thick enough to maintain tissue integrity and provide consistent staining, yet thin enough to permit clear light transmission and avoid steric issues that can blur the birefringence. If sections are too thin (2–4 microns), there may be insufficient tissue mass to stain evenly and to reveal the ordered amyloid arrangement. If sections are too thick (15–20 or 50 microns), dye penetration becomes uneven and light transmission is impeded, which can obscure the characteristic birefringence and produce uneven staining. Therefore, about 8–10 microns is the optimal thickness for Congo Red staining of amyloid.