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YOUR STUDIO NOTEBOOK

Clay test log.

Keep each clay body’s measurements and firing conditions together. Compare drying, firing and total linear shrinkage, then use a completed test in the calculator.

Saved tests stay only in this browser on withcalculator.com. Entries saved on clay.withcalculator.com do not transfer automatically; your old staging log remains separate.

Prefer paper? Print a clay shrinkage test card for measurements, firing conditions and studio notes. Entries on the card are not saved.

Private to this browser

Records are stored only in this browser profile’s local storage. They are not uploaded, synced, included in URLs, or sent with analytics. Clearing browser data or switching profiles/devices can remove or hide them. Download a JSON backup for restore in this root log, or export CSV for spreadsheets and local CSV import. Backups contain your private measurements and notes; keep them somewhere safe. No file is uploaded during restore. Storage errors switch this page to temporary in-memory records; those disappear when you leave or reload. Corrupt saved data is never overwritten automatically.

Add a test

Changing units converts entered lengths.

Drying % = (wet − dry) ÷ wet × 100. Dry-to-fired % = (dry − fired) ÷ dry × 100. Total wet-to-fired % = (wet − fired) ÷ wet × 100. Each rate uses its own starting length; do not add stage percentages. Equal lengths mean 0% shrinkage. Expansion is not supported.

Mark two points on a small test bar. Measure the same marks when wet, bone-dry, and after the final firing once cooled; use the same body, forming method, and firing process for meaningful comparisons. Results vary with clay and process; keep tests separate rather than averaging different conditions. See Digitalfire’s shrinkage test.

JSON backup & restore

Download a JSON backup before clearing browser data, changing device or restoring another file. JSON preserves record IDs and can be restored here; CSV export remains available above for spreadsheets and the separate CSV import below. Files are processed only on this device, never uploaded.

Close other tabs using this log (especially older open copies) before restoring. Restore only an unmodified JSON backup from this root test log (schema v1, up to 5 MB / 5,000 records per file). Old clay.withcalculator.com files are not supported. Restore adds new IDs only: duplicate IDs are skipped and reported, even when their contents differ. Existing records are never replaced or deleted.

Clear-data warning: Clearing this browser’s site data or using “Clear all records” can permanently remove your tests. Download a JSON backup first and keep it privately. A SHA-256 check detects accidental file changes; it is not encryption or proof of who created a backup.

Import CSV exports

Bring back a CSV downloaded with this tool’s Export CSV button. Processing stays entirely on this device; no file or measurements are uploaded. Download a JSON backup first and close other log tabs. Import only adds new records; it never replaces or deletes existing tests.

Supported CSV format and duplicate rules

UTF-8 comma-separated CSV, with or without a BOM; CRLF or LF line endings; double-quoted fields, doubled quotes and multiline notes are supported. Maximum 5 MB and 5,000 data rows (also 5,000 records total). Use the original values, not spreadsheet-formatted or rounded percentages.

Required headers in this exact order: Clay body, Test label, Date, Unit, Wet length, Dry length, Fired length, Drying shrinkage %, Dry-to-fired shrinkage %, Wet-to-fired shrinkage %, Cone / temperature, Schedule / atmosphere. New exports add a final Record ID column; older 12-column exports are also accepted. Unknown or reordered headers and broken CSV quoting reject the whole file. Other malformed rows are skipped and explained by starting line number.

Dates must be real YYYY-MM-DD dates; units mm, cm or in. Wet length must be positive; dry/fired may be blank, otherwise positive and no greater than the previous stage. Percentages must match the lengths. Body and label are required (120 characters each); cone/temperature allows 120 and notes 1,500. Blank optional values stay blank.

A nonblank Record ID is used for deduplication: repeated IDs are skipped even when content differs. Without an ID, an exact fingerprint of body, label, date, unit, all lengths, cone and notes is used; identical rows are skipped and other valid rows receive new IDs. Text, spacing and units are not normalized. Legacy CSV cannot distinguish intentionally separate identical tests. A leading apostrophe used by this exporter before =, +, @ or - is removed from text fields; legacy CSV cannot distinguish that escape from an intentionally typed apostrophe. Prefer JSON backup for exact identity and text preservation. CSV has no integrity checksum or proof of origin.

Your tests

No tests recorded yet. Add your first test above. No sample records are preloaded.