--- title: Metal Corrosion description: Understand how temperature and humidity in your spaces affect the corrosion risk of metal objects. --- [Skip to content](https://support.conserv.io/knowledge/metal-corrosion#main-content) English Show submenu for translations [Contact us](https://support.conserv.io/knowledge/kb-tickets/new?hsLang=en) [![Cnsrv\_wmM\_mix\_rgb - MEDIUM-1.png\]](https://support.conserv.io/hs-fs/hubfs/Cnsrv_wmM_mix_rgb%20-%20MEDIUM-1.png?height=40&name=Cnsrv_wmM_mix_rgb%20-%20MEDIUM-1.png)](https://conserv.io/) - [Support](https://support.conserv.io/knowledge) - [Blog](https://support.conserv.io/blog) Open main navigation Close main navigation - [Support](https://support.conserv.io/knowledge) - [Blog](https://support.conserv.io/blog) - English Show submenu for translations - [Contact us](https://support.conserv.io/knowledge/kb-tickets/new) - [Contact Us](https://support.conserv.io/knowledge/kb-tickets/new) [Contact Us](https://support.conserv.io/knowledge/kb-tickets/new?hsLang=en) How can we help you? - There are no suggestions because the search field is empty. 1. 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[Preservation Metrics](https://support.conserv.io/knowledge/analytics-and-reports?hsLang=en#preservation-metrics) # Metal Corrosion ## Understand how temperature and humidity in your spaces affect the corrosion risk of metal objects. **Table of Contents** - [What the Metric Measures](https://support.conserv.io/knowledge/metal-corrosion#what-the-metric-measures) - [How the Metric Is Calculated](https://support.conserv.io/knowledge/metal-corrosion#how-the-metric-is-calculated) - [Interpreting the Values](https://support.conserv.io/knowledge/metal-corrosion#interpreting-the-values) - [Limitations and Considerations](https://support.conserv.io/knowledge/metal-corrosion#limitations-and-considerations) - [Related Articles](https://support.conserv.io/knowledge/metal-corrosion#related-articles) - [Additional Resources](https://support.conserv.io/knowledge/metal-corrosion#additional-resources) --- ### What the Metric Measures The metal corrosion metric estimates how much your storage environment contributes to corrosion of metal objects. Lower values mean lower risk. The metric is based on the Maximum Equilibrium Moisture Content (MaxEMC) metric developed by the Image Permanence Institute (IPI). | Property | Value | | --- | --- | | Applies to | Metals | | Measures | Effect of the environment on metal corrosion | | Primary driver | Relative humidity (RH) over time | | Interpretation | Lower is better | Corrosion depends on temperature and RH in complex ways. These conditions affect both how fast corrosion happens and whether it happens at all. These complexities make a full corrosion model impractical, so MaxEMC is used as an approximation that accounts for exposure time and, primarily, RH. ### How the Metric Is Calculated The metric converts lagged temperature and RH readings into equilibrium moisture content (EMC), then reports the highest EMC value in the selected period. 1. Collect temperature and RH readings from the sensor. 2. Calculate a 24 hour running average of temperature. 3. Calculate a 30 day running average of RH. 4. Convert each pair of averaged values to %EMC using the United States Forest Products Laboratory (USFPL) equations for an average species of wood. 5. Select the highest %EMC value in the period. *The highest %EMC value is the metal corrosion metric (MaxEMC).* The running averages model the time lag between a change in the room and the response of the objects, as the impact of environmental changes on an object's moisture content are not immediate. **Note:** RH has a much larger effect on EMC than temperature. A sustained period of high RH raises the metric more than a short spike. ### Interpreting the Values A metal corrosion value below 7% indicates a good environment for metal objects. Values above 10.5% indicate risk. | MaxEMC | Rating | Meaning | | --- | --- | --- | | Less than 7% | Good | Low corrosion risk | | 7% to 10.5% | OK | Moderate corrosion risk | | Greater than 10.5% | Risk | Elevated corrosion risk | *Table from: Nishimura, D. W. (2011, April). Understanding Preservation Metrics. Rochester; Image Permanence Institute.* **Tip:** If the metric is in the Risk range, review the RH history for the period. Sustained high RH is the most likely cause. ### Limitations and Considerations **Important:** The metric is an approximation of corrosion risk, not a direct measurement of corrosion. - The EMC equations describe an average piece of wood, not metal. EMC is used as a proxy for the combined effect of RH and exposure time. - The metric uses only temperature and RH. It does not include other factors, such as pollutants or the type of metal. - The metric reports the worst point in the period. A single sustained humid stretch sets the value, even if the rest of the period was dry. - The metric applies to the environment the sensor measures. Conditions inside enclosures or display cases may differ. - A low value does not guarantee that corrosion will not occur.   **Caution:** Always interpret preservation metrics together with knowledge of your collection. ### Related Articles The metal corrosion metric is one of several preservation metrics in Conserv Cloud Analytics. - [Understand Preservation Metrics](https://support.conserv.io/knowledge/understand-preservation-metrics?hsLang=en) - [Mold Risk Score](https://support.conserv.io/knowledge/mold-risk-score?hsLang=en) - [Time-Weighted Preservation Index](https://support.conserv.io/knowledge/time-weighted-preservation-index?hsLang=en) ### Additional Resources - The MaxEMC metric is explained in the Image Permanence Institute document [Understanding Preservation Metrics](https://www.rit.edu/ipi/sites/rit.edu.ipi/files/documents/understanding_preservation_metrics.pdf). - For background on the IPI metrics, see [Context, Development, and Intent: An Introduction to the IPI Preservation Metrics](https://www.mdpi.com/2571-9408/6/5/221) by Emma J. 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