How-to · Preparation
Prepare a Green River fish plate
Split-fish from the 18-inch layer are prepared with a needle and patience; the trick is stopping at the bone.
1. Know which layer you have. Fish from the split-fish layers (the quarry layers most pay-to-dig sites work) are visible when the slab is split and prepared by removing a thin skin of matrix from the bone. Fish from the 18-inch layer are buried in the slab and need to be located and uncovered; they take ten times as long and are usually sent to a preparator.
2. Stabilise the slab first. Trim it square on a tile saw if you have one (wet, slow), then glue any cracks from the back with Paraloid B-72 at 25 % in acetone or, for a working plate, a thin epoxy on the reverse only. Let it cure a day. Do not consolidate the fish face yet.
3. Work under a lamp at a low angle with a head-loupe or a stereo microscope. Start at the tail with a pin vice and a sharpened needle: drag the point along the surface so the matrix flakes up and away from the bone. The bone is darker, denser and slightly glossy; the matrix is pale and chalky. When the needle skates instead of bites, you are on bone.
4. Move to the fins and the rays. Fin rays are the parts most often destroyed and the parts an expert looks at first. Follow each ray with the needle; do not cross rays. The skull comes last and takes the longest: work from the edge of the bone inward, never across the sutures.
5. Brush away the dust often with a soft brush and blow gently; do not blow with your mouth on a plate you have consolidated (moisture). An air-abrasive unit with sodium bicarbonate at 20–30 psi tidies the surface after needle work and is optional; it also softens the crisp look, so keep it brief.
6. When the fish is uncovered, consolidate the bone only with 3–5 % B-72 in acetone applied with a fine brush; it darkens the bone slightly and holds the scales. Do not coat the matrix (it looks varnished) and do not use anything you cannot remove.
7. Missing parts stay missing. If you fill or inpaint a fin, record the location and the percentage on the Preparation tab and disclose it on the card. A wholly natural, unrestored plate is worth more than an inpainted “perfect” one to any buyer who knows the layer.
8. Record the layer, the quarry and the date on the record with the quarry receipt in the vault; it is the difference between a fish and a fish with provenance.
Sources
Cite this article
Stratum Study. "Prepare a Green River fish plate" (How-to). Stratum Study pack 2026.09, as of 2026-09-16. https://stratum.black/study/how-to/prepare-a-green-river-fish-plate. Accessed 2026-09-20.
@misc{stratum-prepare-a-green-river-fish-plate,
title = {Prepare a Green River fish plate},
author = {{Stratum Study}},
howpublished = {\url{https://stratum.black/study/how-to/prepare-a-green-river-fish-plate}},
year = {2026},
note = {How-to article, Stratum Study pack 2026.09, as of 2026-09-16; sources: stratum. Accessed 2026-09-20.}
} Citations carry the pack version and the article's as-of date so they resolve to the same text later. The facts themselves belong to the sources listed below; cite those for the science.