06 February 2012

Mosaic Process - Working With Stone

I've had a few people ask about my process for working with stone in mosaics recently.

Creating a mosaic with stone differs from other mosaic work mostly in the way that you cut the tesserae.

How I do it:

Disclaimer - I am not an expert, yet. I'm just telling you what works for me.

Most of the stone I use starts out as floor tiles. They run from 7/16" to 5/8" thick and are usually 12" x 12" in size. Sometimes I'll get the smaller ones, but there is more waste per piece with them since I trim off all the outer smooth-cut edges.

Top to bottom: 3 shelves of cut stone tesserae,
uncut stone tiles & slabs, bins of cut-up chunks

I cut the tile into manageable chunks - trying to get the chunks as rectangular as possible - with a hammer and hardie. I don't like manufactured edges to show in my mosaics, so I cut the stone to the point where the tessera has the "footprint" that I want and then I turn it sideways and cut it in half. This allows me to turn all the manufactured edges down and have only the hand-cut, irregular edges showing.

Hammers & Hardies, left - steel hammer & hardie for cutting stone,
right - carbide-tipped hamnmers and hardie for cutting glass
Stone cutting process - note the progressively smaller cuts. The two
small pieces on the top of the stack are ready for use in a mosaic.

You want to develop enough control that the force of the hammer-fall is transmitted just to the stone. There are two methods of swinging the hammer: to pivot at the elbow joint, or to pivot at the wrist. I try to isolate the pivot in my elbow joint. I find that it saves my wrist from the shock (important since I have some joint issues from earlier injuries). It also feels like I have more control and I don't fatigue so quickly.

When you're using a hammer and hardie it's important to avoid striking the hardie with the hammer as much as possible. It really dulls both the hardie and the hammer when it happens. I get the best cuts when I focus on making sure that I strike the stone exactly above where it rests on the hardie - so that the hammer tip is directly above the cutting edge of the hardie.

If I'm working with a very crumbly stone (soft limestone/sandstone) or stone that is prone to irregular cuts (heavily veined marble), I'll cut the tessarae using the hammer & hardie down to a certain size and then use my compound tile nippers or a CHEAP pair of glass tile nippers - not my Leponitts or my Montolits - to make the final cut. I have to admit that feels a bit like cheating... but I don't like wasting material and time.

I usually mix stone and glass in the mosaics. I like the rough stone and the smooth and shiny glass side-by-side. I also like the contrast between the subtle, muted colors of the stone and the more intense, pure colors of the glass.

Dalle de verre and found glass

The glass is usually dalle de verre with some smalti and the occasional weird found glass.  The dalle de verre is cut using carbide-tipped hammer and the hardie. I also use a chipping hammer to distress the surface of any larger blocks of glass and also to create shards to use in the mosaics.

Carbide-tipped hammers and hardie. Top: chipping hammer. Bottom: cutting hammer
Cutting dalles.
The carbide tips are more brittle than the steel surrounding them. It is important to always strike the glass with the hammer lined up straight with the hardie just in case you pass all the way through the glass and strike the hardie.

This is what happens when your carbide hammer strikes the hardie unevenly.
The chipping hammer isn't used with the hardie. The cut piece of dalle de verre is laid on its side and you strike it with the hammer at an angle, trying to catch just the edge of the piece of glass. This process takes off the manufactured, flat surface and creates a more visually interesting piece of glass.

The top of the smaller piece of dalle de verre has been distressed using the chipping hammer.

I use mostly Wediboard for substrate. For the stone mosaics I use the 5/8" instead of the 1/2", mainly because of the finished weight. I have a local (well, within 150 miles) supplier for the wediboard, Cole Papers in Minneapolis. They don't list wediboard on their website, but they do sell it.

I use thinset mortar to adhere the stone and glass to the Wediboard. I've been using Mapei Keraset mortar, mixed with a 1:1 mixture of water and Mapei Keraply. I'd use Laticrete products, but I can purchase the Mapei products locally.

I color the mortar with Gamblin dry pigments or Sheffield Tints-All. Lately I've been mostly using the Gamblin but I stay away from the cadmium, chromium and cobalt pigments. I don't have a safe ventilation system for using them.

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