If the OFM will pardon the AI, Grok is quite familiar with TMP and offered this: (the references do not copy but half of this the AI lifted from TMP)
Glasses on a miniature are finicky because the frames are tiny and the lenses need to read as glass rather than painted plastic, but they are very doable with a fine brush, steady hands, and a magnifying lamp or optivisor.
Practical Painting Approach
Paint the face, skin, and eyes completely first (including any shading and highlights). This lets you clean up overflow from the frames later with flesh color. Use a good #00 or finer brush and thinned paint so the frames stay crisp.
Frames:
Wire-rimmed spectacles (the most common Old West look for a refined or gambler type) work well in black, dark gray, or a metallic like silver/steel.
Paint the thin lines carefully. Dry-brushing or careful edge highlighting can help them catch light.
Expect some mistakes—touch them up immediately with the skin tone.
Lenses (the part that sells the effect):
Several reliable methods exist:
Simple tabletop: Base the lens area in a light flesh tone (or a pale blue-gray). Add a thin line and a small white/light-gray dot for a specular highlight, then finish with gloss varnish. This creates a convincing transparent look at gaming distance.
Reflective/glass effect: Base with a metallic (silver or steel), build a subtle gradient, then apply a transparent tint, ghost tint, clear paint, or thinned contrast/speedpaint. Gloss varnish seals it. This mimics real reflections better.
Gem-style gradient: Treat each lens like a small gem—dark base at the top, mid-tone toward the bottom, lighter highlight, and a pure white specular dot in the opposite corner. Finish with gloss. High contrast sells the shine.
Gloss (or a satin + gloss on just the lenses) is essential for the glass read. Avoid heavy washes over the finished lenses or they lose definition. If the miniature has open (hollow) lenses rather than solid ones, the same principles apply—just be extra careful with the frames.