## Scope
Manual (non-electric, non-piercing) facial skin tools for home use — stone/metal rollers, gua sha scraping tools, and ice rollers/globes; excludes electric LED/microcurrent devices and microneedling/derma rollers (separate, regulated category).

## Seed
1. Equivalent of the hardness/toughness trade-off: natural crystal (jade/rose quartz/amethyst/obsidian) gives symbolic weight and natural coolness but chips/cracks and loses warranty coverage if dropped or frozen; stainless steel/resin give that up for drop- and freezer-safe durability.
2. An allergist would notice first: "jade" rollers are frequently dyed quartzite, marble, or glass rather than tested gemstone, and no listing discloses this or the tool's metal alloy — both are hidden-material exposure questions, same logic as reading an ingredient list.

## Sources
- [wikipedia_gua_sha] https://en.wikipedia.org/wiki/Gua_sha — materials/technique/safety — fetched excerpt: "ceramic spoons, coins, jade stones..."; "nearly always causes minor skin trauma...dermatitis"
- [wikipedia_jade] https://en.wikipedia.org/wiki/Jade — jadeite/nephrite, Mohs 6-7, density 2.9-3.38 — fetched excerpt confirms both minerals and treatment types
- [gemsociety_jadeite] https://www.gemsociety.org/article/jade-jewelry-and-gemstone-information/ — jadeite Mohs 6.5-7, SG 3.25-3.36, fakes (dyed quartzite/marble/serpentine/glass) — fetched excerpt
- [wikipedia_cryotherapy] https://en.wikipedia.org/wiki/Cryotherapy — vasoconstriction mechanism, Raynaud/cold urticaria contraindications — fetched excerpt
- [wikipedia_cold_urticaria] https://en.wikipedia.org/wiki/Cold_urticaria — cold objects trigger hives, avoidance is primary management — fetched excerpt
- [mountlai_stone_guide] mountlai.com stone guide — jade/rose quartz/amethyst cool, obsidian warms — fetched excerpt
- [mountlai_care_guide] mountlai.com care guide — stone non-porous myth debunked, disinfectant-safe — fetched excerpt
- [mountlai_lymph101] mountlai.com lymphatic drainage 101 — tool shape hugs contours, under-eye needs light pressure — fetched excerpt
- [mountlai_product_jade_roller] mountlai.com jade roller product page — dual head sizes — fetched excerpt
- [mountlai_product_rq_guasha] mountlai.com rose quartz gua sha product page — curved jaw edge, freezer warranty exclusion, oil/serum use — fetched excerpt
- [mountlai_product_obsidian_roller] mountlai.com obsidian roller product page — warmth retention, dual head — fetched excerpt
- [mountlai_product_ss_guasha] mountlai.com stainless steel gua sha product page — non-porous, drop-resistant, acne-prone fit — fetched excerpt

## Branches
- tool_type=facial_roller → roller_head_configuration, stone_or_material; makes gua_sha_edge_profile/cold_contraindication_risk irrelevant — per mountlai product pages (roller-specific head sizing, no edge shape).
- tool_type=gua_sha_tool → gua_sha_edge_profile, stone_or_material; makes roller_head_configuration/cold_contraindication_risk irrelevant — per mountlai_lymph101 (edge/curve usage per zone).
- tool_type=ice_roller_or_globe → cold_contraindication_risk; makes roller_head_configuration/gua_sha_edge_profile/material_authenticity irrelevant — per wikipedia_cryotherapy (cold-specific safety, no stone-authenticity question applies to a metal/gel ice head).

## Noise
- Price, shipping, warranty-registration mechanics (mountlai product pages) — commerce, not an expert differentiator; price is never a facet.
- "What's inside" / tutorial guide included — packaging detail, not a product-judging spec.
- Jade massaging comb (scalp/hair tool on mountlai) — different leaf (hair tools), not a facial tool.
- Vitality Qi LED gua sha/roller devices — site itself splits "LED Devices" from "Gua Sha Tools"; electric device, out of this leaf's scope.
- Derma rollers / microneedling — FDA-adjacent regulated medical device category (needles), not a manual massage/scraping tool; separate leaf.
- Stone symbolism copy (eternal youth, self-love, tranquility) — marketing/spiritual framing, not a testable expert judgment; kept only the thermal/durability facts from the same source.
- Handle length/grip (Cosmopolitan reviewer call-outs, "long handle = great grip" vs "could have been bigger") — ergonomic preference, not a hard spec threshold; left out rather than added as a facet.

## Corrections (2026-10-26)
- Added a third `primary_goal` branch for `tension_and_lymphatic_release` (`then_ask: gua_sha_edge_profile`), which had no branch at all despite the split's own rationale promising it one.
- Broadened `skin_sensitivity_fit` with a `medical_contraindication_consult_doctor` value and rewrote its `why_experts_care`/`backfill_note` to carry blood-thinner, clotting-disorder, pregnancy, eczema/psoriasis/rosacea, and recent-cosmetic-procedure cautions, per healthline_guasha.
- Added a `bian_stone` value to `stone_or_material`, backed by cosmo_guasha_buyers_guide ("Stone type: Bian" on 2 of 9 picks) and wikipedia_bian_stones.
- Changed `source` from `listing` to `researched` on `stone_or_material`, `roller_head_configuration`, and `scale_and_target_area`, since only Mount Lai's own pages (not a third-party retail listing) back the "usually in the title" claim; softened each `listing_field_hint` accordingly.
- Added an `Amethyst` vocabulary entry for parity with its sibling stone values.
- Added a `Bian stone` vocabulary entry for the new facet value.
- Split the "Dyed or treated quartzite" vocabulary entry into "Imitation jade (dyed quartzite)" (covers `imitation_substitute`) and "Treated or dyed jade" (covers `treated_or_dyed`), since the original only anchored one of the two values.
- Changed `skin_sensitivity_fit`'s `backfill_cost` from `medium` to `low`, matching its own flat-default backfill_note and the same pattern used for `cold_contraindication_risk`.
- Rejected nothing from the Required fixes list; all 8 items (including the minor handle-length one, via the Noise line above) were addressed.