To use oxalic acid on rocks, you typically mix it with water to create a solution for cleaning, especially to remove iron and rust stains.
Preparing the Oxalic Acid Solution
According to guidance, a general starting point for preparing an oxalic acid solution for cleaning rocks is:
- Use about 2 tablespoons of oxalic acid to ½ gallon of water.
It's important to note that the optimal amount of oxalic acid can vary considerably depending a lot on the specimen to be cleaned. This means you might need to adjust the concentration based on the specific rock type, the severity of the staining, and the rock's porosity.
Caution: Using too much oxalic acid in the solution can potentially cause the rock specimen to turn yellow.
Applying the Solution to Rocks
Oxalic acid is commonly used by mineral collectors and geologists to clean mineral specimens and rocks, primarily for removing iron and rust stains that can obscure the specimen's natural beauty.
Here's a basic approach to applying the solution:
- Mix the Solution: Carefully dissolve the oxalic acid crystals or powder in the specified amount of water. Use a container made of plastic or glass (avoid metal).
- Submerge or Apply: Place the stained rock specimen into the prepared oxalic acid solution, ensuring it is fully submerged. For very large rocks, you might need to apply the solution directly using a brush or cloth, keeping the surface wet.
- Soak: Allow the rock to soak in the solution. The necessary soaking time can vary greatly, from a few hours to several days, depending on the stain's intensity and the rock's composition. Monitor the process regularly.
- Rinse Thoroughly: Once the stains have been removed to your satisfaction, it is crucial to rinse the rock very thoroughly with clean water to remove all traces of the oxalic acid. Multiple rinses or soaking in clean water for a period might be necessary. Incomplete rinsing can lead to residues or potential long-term damage or discoloration.
Important Considerations
- Specimen Sensitivity: Different rocks and minerals react differently to acid treatments. Always test the solution on a small, inconspicuous area first if the specimen is valuable or delicate.
- Concentration Adjustment: As mentioned, the 2 tablespoons per ½ gallon ratio is a starting point. If stains are stubborn, you might increase the concentration slightly, but always be mindful of the risk of yellowing or other damage. If stains are light, a weaker solution might suffice.
- Ventilation: Oxalic acid can release fumes, so always work in a well-ventilated area, preferably outdoors or under a fume hood.
By carefully preparing the solution using the suggested ratio (adjusting as needed based on the specimen) and applying it correctly, you can effectively use oxalic acid to clean stains from rocks while minimizing the risk of adverse effects like yellowing.
