Ceramic Temper Analysis Calculator
Analyze ceramic thin section point counts to determine temper type, proportion, and porosity.
About this calculator
Ceramic petrographic analysis identifies what a potter deliberately mixed into raw clay before firing — sand, crushed shell, ground-up sherds (grog), or other temper — because that choice of material and proportion is a cultural signature that can distinguish production traditions, trace trade networks, or separate local wares from imports. Analysts examine a thin section of the ceramic fabric under a petrographic microscope and tally what each of several hundred counted points lands on: a temper mineral, the surrounding clay matrix, or a void. This calculator takes those raw point counts and converts them into the percentages archaeologists actually compare — total temper percentage, clay matrix percentage, and porosity — plus identifies which temper type dominates and which is the secondary constituent.
Porosity, the percentage of points landing on voids, is itself diagnostic: high porosity often signals poor firing or the burn-out of organic temper (chaff, grass, dung) that leaves empty channels behind, while low porosity generally indicates a well-fired, well-compacted fabric. None of this substitutes for the analyst's own mineral identification under the microscope — the calculator only turns confirmed point-count tallies into the summary statistics used in a ceramic petrography report.
Inputs
Results
Dominant Temper
Quartz/Sand
Porosity Assessment
Low (well-fired)
How to Use This Calculator
- Enter Total Points Counted, Quartz / Sand, and Feldspar.
- Set Mica, Shell, and Grog (crushed pottery).
- Adjust Voids / Pores as needed.
- Review Dominant Temper and Porosity Assessment.
- Use Total Temper % and Clay Matrix % to inform your decision.
What each input means
- Total Points Counted
- Total point count in the thin section analysis.
- Quartz / Sand
- Points identified as quartz or sand grains.
- Feldspar
- Points identified as feldspar minerals.
- Mica
- Points identified as mica flakes.
- Shell
- Points identified as crushed shell.
- Grog (crushed pottery)
- Points identified as recycled ceramic fragments.
- Voids / Pores
- Empty spaces and pore points.
How this is calculated
Worked example, using the default values
- Identify Input Parameters7 parametersTotal Points Counted = 200, Quartz / Sand = 40, Feldspar = 10, Mica = 5, Shell = 15, Grog (crushed pottery) = 0, Voids / Pores = 12 = 7 input(s) provided
- Calculate Dominant TemperDominant TemperQuartz/Sand = Quartz/Sand
- Calculate Porosity AssessmentLow (well-fired) = Low (well-fired)
- Calculate Total Temper %Total Temper %35 = 35
- Calculate Clay Matrix %Clay Matrix %59 = 59
Engine last updated . Checked against 3 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
What counts as "temper" versus "matrix" in a thin section?
Temper is the material deliberately or naturally added to raw clay before firing — sand, crushed shell, mica, or grog (crushed recycled pottery) — while matrix is the fine-grained clay body surrounding those inclusions. Distinguishing the two under a microscope is the core task of ceramic petrography, and this calculator only tallies point counts an analyst has already classified.
Why does high porosity matter for interpreting a sherd?
High void content often results from organic temper, like chaff, grass, or dung, burning out during firing and leaving empty channels behind, or from incomplete firing that never fully sintered the clay. Both are meaningful production choices or process outcomes, so porosity percentage is reported alongside temper composition rather than treated as noise.
How many points should be counted for a reliable result?
Ceramic petrography conventionally counts at least 200-300 points per thin section to keep the percentage estimates statistically stable; counting far fewer points inflates the influence of any single misclassified grain. This calculator accepts counts from 50 to 1,000, but results from the low end of that range should be treated as preliminary.
Can two sherds with the same dominant temper still be from different traditions?
Yes. Dominant temper type is only one axis of comparison — the relative proportions of secondary tempers, grain size, sorting, and matrix color all factor into distinguishing production traditions or sourcing sherds to a specific workshop. This calculator reports the composition percentages an analyst needs, not a final attribution.
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