How this desalination schedule calculator works
Artifacts recovered from marine or brackish environments are typically saturated with dissolved salts. If an object is allowed to dry while salts remain, crystals can form inside pores and cracks, causing mechanical damage (for example, spalling in ceramics, delamination in wood, and accelerated corrosion in metals). A common conservation approach is desalination by repeated soaking: the artifact is placed in fresh water, salts diffuse out into the bath, and the water is replaced on a regular schedule.
This planner estimates how many water changes you may need to reduce an initial internal salt concentration (in ppm) down to a target concentration. It also estimates total time and total fresh-water volume used, based on your chosen soak interval and tank volume. The output is intended for planning and documentation; it does not replace chloride testing or professional conservation judgment.
Inputs and units
- Initial salt concentration (ppm): starting concentration inside the artifact (parts per million).
- Target concentration (ppm): desired concentration before moving to the next treatment step or controlled drying.
- Removal efficiency per water change (%): the fraction of remaining salt removed each time you replace the water. This is a simplified parameter that bundles diffusion, porosity, temperature, agitation, and drainage effectiveness.
- Fresh water per soak (L): the volume of fresh water used for each soak cycle.
- Days per soak: how long each soak lasts before you change the water.
Model, formula, and assumptions
The calculator uses a simple exponential (geometric) decay model. If C0 is the initial concentration and r is the removal efficiency per change expressed as a decimal (for example, 30% → 0.30), then after n water changes the concentration is:
Cn = C0 × (1 − r)n
Solving for the number of changes needed to reach a target concentration Ct gives:
n = ln(Ct / C0) ÷ ln(1 − r)
The planner rounds up to the next whole water change because you can’t perform a fraction of a change in practice. It also assumes each change is performed on schedule, the artifact drains reasonably between baths, and the “efficiency” stays constant. Real objects may desalinate more slowly in dense regions or enclosed cavities, so treat the estimate as a baseline.
Worked example (matches the default values)
Suppose a waterlogged wooden artifact is estimated at 20,000 ppm salt internally, and you want to reach 500 ppm. If each water change removes about 30% of the remaining salt, and you change 50 L of water every 3 days, the model predicts about 12 water changes. That corresponds to roughly 36 days of soaking and about 600 L of fresh water. Use the CSV download to save the assumptions in your project notes.
Practical tips for conservators and field labs
- Validate with testing: periodic chloride or conductivity measurements of the soak water can confirm whether your assumed efficiency is realistic.
- Temperature and agitation: warmer water and gentle circulation often increase removal efficiency, but may increase biological growth risk.
- Water quality: deionized or distilled water reduces the chance of introducing new minerals; cover tanks to reduce evaporation and contamination.
- Scheduling constraints: if changes only happen on certain days (weekends, staffing limits), set “Days per soak” to reflect your actual cadence.
- Limitations: composite objects (metal + wood, laminates, concretion) may require separate or staged treatments; consult a conservation specialist.
Related planning tools
If you are budgeting water production or treatment in remote locations, you may also find these pages useful: Reverse Osmosis Desalination Energy Cost Calculator, Ancient Manuscript Silica Gel Humidity Buffer Calculator, Museum Artifact Light Exposure Budget Planner, and Portable Darkroom Waste Neutralization Planner.
Understanding artifact desalination (background)
When archaeologists retrieve artifacts from the ocean, the items are saturated with salt water. Salt crystals forming during drying can crack ceramics, delaminate wood, and corrode metal. Before an artifact can be safely displayed or stored, conservators must remove the salt by soaking the object in successive baths of fresh water. Each water change leaches some of the dissolved salts from the artifact’s pores into the bath. Planning the number of changes is more complicated than simply repeating the process until tests show low salt: fresh water is expensive to transport to field labs, and extended soaking increases the risk of biological growth or material degradation. A quantitative estimate helps schedule labor, provision water, and manage preservation risks.
This calculator models desalination as an exponential decay process. In each soak, a fixed fraction of the remaining salt diffuses out of the artifact and into the surrounding water. The fraction depends on factors such as artifact porosity, surface area, water temperature, and whether the water is agitated. By representing these complexities with a single efficiency percentage, the model remains flexible while providing useful estimates. Users can adjust the efficiency based on experience or small-scale tests.
Comparison table (illustrative)
The table below compares the baseline example with alternative strategies. These scenarios are illustrative; your project’s efficiency may differ.
| Scenario | Removal efficiency | Water per soak (L) | Changes |
|---|---|---|---|
| Baseline | 30% | 50 | 12 |
| Alt A: heated/agitated water | 45% | 50 | 8 |
| Alt B: larger tank | 30% | 100 | 12 |
Increasing removal efficiency through heating or gentle agitation can cut the number of changes, saving time and labor. Using a larger tank does not reduce the number of changes directly in this simplified model, but it increases water consumption, which may be feasible for well-resourced labs. Tables like this help conservators weigh trade-offs between time, water usage, and equipment complexity.
Extended guidance and limitations
Desalination is just one step in artifact conservation. Wood items often require subsequent polyethylene glycol impregnation to prevent shrinkage, while metals may undergo electrolysis or chemical stabilization. Planning soak schedules in conjunction with these treatments helps keep facility throughput steady and avoids bottlenecks. Recording each artifact’s desalination history also aids research, allowing historians to correlate treatment parameters with long-term preservation outcomes.
Conservators sometimes perform quick chloride tests on soak water to monitor progress. The calculator’s output offers a starting estimate, but test results should guide adjustments. If concentrations plateau above target despite many changes, efficiency may be lower than assumed, perhaps due to dense grain or occluded cavities. Conversely, faster-than-expected desalination allows early completion, freeing tank space.
Fresh water quality matters. Using deionized or distilled water minimizes new mineral deposits. In remote field camps where water is scarce, planners might recycle desalination water through reverse osmosis systems. Such setups can draw on tools like the Reverse Osmosis Desalination Energy Cost Calculator for energy budgeting. Other related conservation resources include the Ancient Manuscript Silica Gel Humidity Buffer Calculator, the Museum Artifact Light Exposure Budget Planner, and the Portable Darkroom Waste Neutralization Planner—all useful for managing preservation environments.
Scheduling labor is another consideration. Long soak durations may conflict with staff availability, especially in volunteer-driven projects. The planner’s interval parameter allows simulation of weekend-only work or continuous operations. Keeping soak tanks covered reduces evaporation and contamination. Where biological growth is a concern, mild biocides or more frequent water changes may be necessary; adjust the removal efficiency accordingly if such measures accelerate desalination.
The model assumes uniform salt distribution and removal, which may not hold for artifacts with complex shapes or multiple materials. Combined metal-wood objects often require separate treatments for each component. Some fragile items cannot withstand prolonged soaking and instead use alternative methods like poultices or solvent exchange. Always consult a conservation specialist before applying any treatment.
Temperature affects diffusion rates; warmer water generally increases efficiency but may promote microbial growth. Agitation enhances salt migration but must be gentle to avoid mechanical damage. Documenting exact conditions—temperature, agitation method, and chemical additives—alongside the planner’s calculations improves reproducibility and future research value.
Finally, consider the sustainability of water usage. Transporting hundreds of liters to remote excavation sites can be costly and environmentally challenging. Planning helps minimize waste and encourages creative reuse strategies. By quantifying desalination needs, this planner supports responsible stewardship of cultural heritage recovered from the depths.