Growing transparent calcite crystals on marble to heal cracks – how to suppress cloudy precipitation?

Hi everyone,

I’m a graduate student working on an art–science project, and my goal is to grow transparent calcite crystals directly on marble, specifically inside and along cracks, in a way that mimics natural calcite vein formation and stone “healing”.

The final aim is not just precipitation, but optically clear or translucent calcite growth that could realistically contribute to crack repair.

Before moving to a large aquarium setup with a cracked marble block, I tested seeded growth in a beaker using a ~5 mm calcite seed. I attempted to create a supersaturated solution by slowly mixing CaCl₂ and NaHCO₃ under gentle stirring. However, once all the NaHCO₃ was added, the solution became cloudy, indicating extensive bulk nucleation rather than controlled crystal growth.

My solution preparation was:

• CaCl₂·6H₂O: 2.22 g in 175 mL distilled water (0.1 M)
• NaHCO₃: 0.84 g in 175 mL distilled water (0.1 M)

NaHCO₃ solution was added slowly to the CaCl₂ solution while stirring gently, then stirring was stopped.

From this experiment, I realized that microcrystalline CaCO₃ precipitation is easy to achieve, but this does not produce transparent material nor mechanically meaningful bonding for crack repair.

I’m now planning to scale up to an aquarium-sized system with marble, and I would really appreciate advice on the following:

• Is direct mixing of CaCl₂ and NaHCO₃ fundamentally unsuitable for growing transparent calcite, even with slow addition and stirring?
• Would a bicarbonate-based approach (e.g. Ca(HCO₃)₂ solution with slow CO₂ degassing, like cave speleothem formation) be more appropriate for clarity and larger crystal growth?
• How can bulk nucleation be suppressed while encouraging growth on marble surfaces or within cracks?
• Are gel diffusion or low-convection systems commonly used for this purpose?

Any insight from people experienced in carbonate geochemistry, crystal growth, or stone conservation would be greatly appreciated.
Thank you very much!c