Pottery Clay Reclaim Calculator
Created by: Daniel Hayes
Last updated:
Calculate how to reclaim and recycle your pottery clay scraps, including water adjustments, drying time estimates, and cost savings versus buying new clay.
Pottery Clay Reclaim Calculator
PotteryCalculate water adjustments, drying time, and cost savings for reclaiming pottery clay scraps and trimmings.
What is a Pottery Clay Reclaim Calculator?
A pottery clay reclaim calculator helps potters determine how to recycle their clay scraps, trimmings, and slurry back into usable throwing or hand-building clay. Every potter generates waste clay during the making process, from trimming shavings and throwing slurry to failed pieces and dried-out scraps. Rather than discarding this material and buying new clay, reclaiming allows you to recover nearly all of it at no material cost.
The key challenge in reclaiming clay is getting the moisture content right. Dry scraps need water added, wet slurry needs water removed, and the final product must reach a consistent moisture level throughout. This calculator takes the weight and moisture content of your various scrap types and determines exactly how much water to add or remove to reach your target consistency for throwing or hand-building.
Reclaiming clay is both economically and environmentally sensible. A 25-pound bag of quality stoneware clay costs between 15 and 25 dollars, and a busy studio potter can easily generate 10 to 15 pounds of scrap per week. Over a year, that adds up to hundreds of dollars in potential savings. The reclaim process also keeps clay out of landfills and reduces the demand for raw material mining.
Beyond the practical benefits, many experienced potters believe that reclaimed clay actually throws better than fresh clay from the bag. The additional water exposure during slaking improves the plasticity of the clay particles, and the wedging process aligns the clay structure in ways that make it more responsive on the wheel. Some potters intentionally let new clay go through a reclaim cycle before using it for important pieces.
How the Pottery Clay Reclaim Calculator Works
The calculator first determines the total dry clay content across all your scrap types. Bone-dry scraps contribute their full weight as dry clay. Wet scraps contribute their weight minus the moisture percentage, so a three-pound piece at 20 percent moisture contains 2.4 pounds of dry clay and 0.6 pounds of water. Slurry is assumed to be approximately 40 percent clay solids and 60 percent water by weight, which is typical for throwing slurry collected from the wheel.
Once the dry clay content and existing water are known, the calculator determines how much additional water is needed to reach your target moisture percentage, or how much excess water must be removed. The target moisture formula accounts for the relationship between water weight and total weight. If the result shows excess water, the calculator estimates drying time on a plaster bat based on typical absorption rates. Finally, it calculates cost savings by comparing the reclaimed clay value against the price of buying new clay.
Clay Reclaim Formulas
Dry Clay Content = Dry Scrap + Wet Scrap x (1 - Moisture/100) + Slurry x 0.40
Existing Water = Wet Scrap x (Moisture/100) + Slurry x 0.60
Water Needed = Dry Content x (Target Moisture / (100 - Target Moisture)) - Existing Water
Final Reclaimed Weight = Dry Content / (1 - Target Moisture / 100)
Cost Savings = Reclaimed Weight x $0.72/lb (average new clay cost)
Drying Time Estimate = Excess Water / 0.5 lbs per sq ft per hour
Example Calculations
Example 1: Typical weekly studio reclaim
A potter collects 5 lbs of dry scraps, 3 lbs of leather-hard trimmings at 20% moisture, and 2 lbs of throwing slurry. Dry clay content = 5 + 3 x 0.80 + 2 x 0.40 = 8.2 lbs. Existing water = 3 x 0.20 + 2 x 0.60 = 1.8 lbs. For 22% target moisture, water needed = 8.2 x (22/78) - 1.8 = 0.51 lbs or about 0.06 gallons. Final reclaimed weight is approximately 10.51 lbs, saving $7.57 versus buying new clay.
Example 2: Mostly wet scraps with excess water
A potter has 1 lb of dry scraps, 8 lbs of wet trimmings at 35% moisture, and 4 lbs of slurry. Dry clay content = 1 + 8 x 0.65 + 4 x 0.40 = 7.8 lbs. Existing water = 8 x 0.35 + 4 x 0.60 = 5.2 lbs. For 22% target moisture, water needed = 7.8 x (22/78) - 5.2 = -3.0 lbs. The clay has 3 lbs of excess water that needs to be dried off on a plaster bat before wedging.
Example 3: All dry scraps needing full slaking
A potter has accumulated 15 lbs of bone-dry scraps with no wet clay or slurry. Dry clay content = 15 lbs. Existing water = 0 lbs. For 22% target moisture, water needed = 15 x (22/78) - 0 = 4.23 lbs or about 0.51 gallons. The dry scraps should be covered with water for 24 to 48 hours to fully slake, then dried on a plaster bat to the target consistency. Final reclaimed weight is 19.23 lbs, saving $13.85.
Common Pottery Applications
- Recover throwing scraps and trimmings from daily wheel work to reduce clay purchasing costs.
- Calculate precise water additions when reconstituting bone-dry clay scraps from failed pieces or unused blocks.
- Estimate drying time when reclaiming wet slurry collected from throwing and cleanup.
- Compare the economics of reclaiming versus buying new clay for studio budgeting decisions.
- Plan reclaim batch sizes to match your plaster bat capacity and available drying time.
- Determine whether mixed scraps from different projects need additional water or need to dry before wedging.
Tips for Better Pottery Results
Keep separate reclaim buckets for each clay body you use. Label them clearly with the clay name and firing temperature. Mixing different clay bodies is the most common reclaim mistake and can lead to cracking, crawling, and structural failures during firing. Even clays that fire at the same temperature may have different shrinkage rates that make them incompatible when blended.
Always let dry scraps fully slake before trying to mix them. Dropping dry chunks into wet clay and wedging immediately creates hard spots that will not hydrate properly. These dry inclusions act as stress points during drying and firing, often causing cracks. Give the dry clay at least 24 hours submerged in water, and ideally 48 hours, before draining and drying to working consistency.
Invest in good plaster bats for drying reclaimed clay efficiently. A well-made plaster bat can absorb a significant amount of water per session and dramatically speeds up the reclaim process. Keep your plaster bats clean and replace them when they develop mold, become too smooth from wear, or start shedding plaster chips into your clay. Plaster contamination in clay causes lime pops during firing that ruin finished work.
Frequently Asked Questions
Can you mix different clay types when reclaiming?
Mixing clay types during reclaim is generally not recommended because different clays have different shrinkage rates, firing temperatures, and thermal expansion coefficients. Mixing earthenware with stoneware, for example, can cause cracking during firing because one body shrinks more than the other. If you must mix, keep the blends to clays within the same firing range and similar shrinkage rates, and test small pieces before committing to a full batch.
How do you slake dry clay scraps for reclaiming?
Place bone-dry clay scraps in a bucket and cover them with water. Let them sit for 24 to 48 hours until the clay fully dissolves into a thick slurry. Do not stir too early, as this can create lumps that resist breaking down. Once the clay is fully slaked, pour off excess water from the top, then spread the slurry on a plaster bat or canvas-covered board to stiffen to a workable consistency.
How does the plaster bat drying method work?
A plaster bat absorbs moisture from wet clay through capillary action. Spread your clay slurry or wet scraps across a clean plaster bat in a layer no more than two inches thick. The plaster draws water out of the clay from the bottom, stiffening it over several hours. Flip the clay periodically to ensure even drying. The clay is ready when it reaches a leather-hard to soft consistency suitable for wedging.
How many times should I wedge reclaimed clay?
For reclaimed clay of the same body type, wedge at least 30 times using the spiral or rams-head method. If you have mixed different batches or the clay has been sitting for a long time, increase to 50 passes to ensure even moisture distribution and remove air pockets. Under-wedged reclaimed clay can contain hard spots, air bubbles, and inconsistent moisture that cause problems during throwing and firing.
Is reclaimed clay as good as new clay?
Properly reclaimed clay can be equal to or even better than new clay for throwing. The additional water exposure and wedging process can improve plasticity because the clay particles become better hydrated and aligned. However, if contaminants like plaster chips, paint, or foreign materials get into the reclaim bucket, the clay quality will suffer. Always keep your reclaim bucket clean and free of non-clay debris.
How long does the clay reclaim process take from start to finish?
The full reclaim cycle typically takes three to seven days depending on your method. Slaking dry clay takes one to two days. Drying on a plaster bat takes another one to three days depending on humidity, clay thickness, and the condition of the plaster. Final wedging takes 15 to 30 minutes. A pug mill can shorten the process to one to two days total because it mechanically mixes and de-airs the clay.
What equipment do I need to reclaim clay at home?
At minimum, you need a five-gallon bucket with a lid, a plaster bat or thick canvas board, and a sturdy wedging surface. A kitchen scale helps you measure weights accurately. Optional but helpful equipment includes a pug mill for mechanical mixing, a wire clay cutter for dividing large blocks, and a spray bottle for moisture adjustments. A screen or sieve is useful for removing debris from the slurry.
Sources and References
- Rhodes, Daniel. Clay and Glazes for the Potter, Revised Edition. Chilton Book Company, 1973.
- Hamer, Frank & Hamer, Janet. The Potter's Dictionary of Materials and Techniques, 5th Edition. A&C Black Publishers, 2004.
- Peterson, Susan & Peterson, Jan. The Craft and Art of Clay, 5th Edition. Laurence King Publishing, 2012.
- Zamek, Jeff. What Every Potter Should Know. Krause Publications, 1999.