Onyx Butterflies

The inlay sections of the base material and the butterflies were cut using a CNC waterjet. This method allows for precise, narrow cuts into the stone. Each stone type was cut independently and then assembled using stone grade epoxy. Once assembled, the surface was flattened and polished.

Cracks & Failed Epoxy

Edge chips

Scratches & Dullness

It's important with a job like this to have a very clear plan for the repair. This requires a firm understanding of the nature of the materials you are working with. The combination of soft marble and harder onyx meant our grinding discs would want to roll over the onyx and dig into the marble, leaving an uneven surface. The addition of epoxy, which is harder than the marble further complicates the repair, jeopardizing evenness of the grind. This could be mitigated by using a heavier machine, but the size of the table, existing cracks,  and fragile base made this very risky. We addressed these concerns by going with a rigid aluminum drive and very rigid diamonds to reduce flexing and keep heavy depressions at bay.

In order to protect the floors and surrounding furniture we used waterproof drop cloths, tape and poly. 

Epoxy was pigmented  on site to match the various areas of the table- black for the edges, honey clear for the onyx.  

As mentioned before, a large, rigid drive was used during the grind to prevent the grinding discs from rolling over the harder onyx and digging into the soft black marble. Grinding is always done with water, it keeps the dust contained as well as prevents overheating the stone and epoxy. Overheating the surface can cause shrinkage or failure of the epoxy, or even introduce new cracks between the two very different types of stone. It's important to note, this process of removing stone can't be undone,  so we chose to start with less aggressive diamonds. It took longer, but allowed for more precision.  

Four grits of progressively smoother diamond grinding discs were used, 400g - 800g - 1500g. The first grind was aggressive enough to level off the epoxy as well as to remove etches, scratches and any other wear present. The next two stages smoothened the scratches of the previous grind and prepared the surface for polishing. We thoroughly cleaned the entire surface between grits to prevent any microscopic pieces of onyx epoxy or diamond from scratching the extremely soft marble during the next steps.

The marble and onyx both responded very well to polishing. A soft white polishing pad was used with non acidic polishing compound. Polishing is done over 4-6 stages. The first stages uses a high concentration of polishing compound and low amount of water, creating a thick slurry. This first step of polishing can almost be considered a final form of grinding, since the compound in high quantities does shave some material away. The next stages of polishing use lower and lower quantities of compound, but increased water. Repeated passes smoothen the surface to high gloss perfection without the use of topical coatings, waxes or other artificial layers applied to the stone. It is a completely mechanical process.

The polishing had done a very good job of bringing the rich black colour of the marble back, but we wanted to see if we could get it even darker. A thin application of colour enhancing sealer was applied, left to penetrate and buffed off. The colour enhancer added around 5% to the darkness of the marble - while this may not a substantial gain, we aim for perfection. We followed the enhancer with a normal, transparent sealer. This next application of sealer was not required, but being less viscous than the enhancer, we figured it would draw deeper into the stone, and further protect the material.