Why obsidian needs a different decision
The US Geological Survey describes obsidian as volcanic glass. Its curved fracture can leave extremely sharp edges. That is a meaningful difference from treating every black stone as ordinary durable tumbling rough: examine the material without running a finger along a broken edge, and keep sharp pieces out of casual handling.
Begin with an identification from the rough supplier or a knowledgeable specialist. A black color alone is not an identification. On your batch card, record whether you have broken obsidian, rounded Apache tears, or a named variety such as snowflake obsidian. Keep that description with the source of the chosen instructions.
Keep the specimen or change its shape?
Make a preservation decision before buying supplies. Photograph the features you value and write down what a successful result would retain: the overall outline, an attractive band, or a particular face. If changing those features would be disappointing, keep that piece as collected and practice with replaceable rough.
Our planning checklist separates three choices. Keep means no abrasive processing. Practice means a modest trial with material you are willing to change. Finish means you already have an appropriate prepared surface and a documented next step. This is an editorial planning aid, not a mineral identification or guarantee of a polish.
Compare complete processes, not isolated grit numbers
RockTumbler.com's obsidian instructions publish separate rotary and vibratory recipes. Their water handling and schedules differ, and the rotary instructions distinguish whole Apache tears from broken pieces. Do not take a water level from one method and a dose or elapsed time from the other. Open the complete source alongside your machine manual before preparing a load.
The supplier's snowflake-obsidian workflow illustrates another material-specific adjustment: it omits coarse grinding, uses abundant ceramic cushioning, and shortens some processing stages compared with its usual harder-stone routine. Those are details of its documented process, not universal settings for every obsidian specimen or machine.
Use an inspection card at each changeover
Build a short comparison record rather than recording only a date. Use the same dry reference face and similar light each time, then choose continue, advance, or remove. Explain the choice in one sentence so the next inspection has something concrete to compare.
- Identity and source: exact rough description, machine, and complete recipe reference.
- Load: material and media included, followed by the manual's weight and fill checks.
- Before: photograph and describe existing edge marks or features you intend to keep.
- After: record changes in outline and any new visible marks; do not judge solely from a wet photograph.
- Decision: identify the next supported action and what observation would make you stop.
Do not buy more polish before describing the problem
A disappointing result should lead to a specific question. Is the issue unwanted shape loss, a new edge mark, or a surface finish that falls short of your objective? Send the supplier the recipe, load notes, and comparison images rather than only asking why the obsidian is dull.
Use our bruising guide for the mechanical-damage investigation and the cleaning guide to review changeovers. The batch journal can retain the decision history. None of these tools replaces the instructions for the machine or proves that a particular stone is ready for another run.
Questions at the workbench
Should I use an agate recipe for obsidian?
Use a documented obsidian process instead. The specialist sources below make material-specific adjustments and distinguish rotary from vibratory operation. A familiar schedule is not sufficient evidence that it suits a different material.
Must every piece of obsidian be polished?
No. Keeping a specimen intact is a valid outcome. Decide what you value about it before exposing it to a process intended to change its surface and outline.
Sources & further reading
- US Geological Survey: Obsidian as volcanic glass and its fracture
- RockTumbler.com: Separate obsidian and Apache-tears tumbling recipes
- RockTumbler.com: Its snowflake-obsidian process
Machine instructions take precedence for its loading, materials, operation, and maintenance. Send a correction.
