Technical tips: Options for tesserae

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By Peter Twining 

This time, Peter Twining takes a look at your options for tesserae, with tips on what’s best – and best avoided – for exterior mosaics. 

Tesserae are the pieces that you add to your substrate to create a mosaic. Whenever you’re choosing a tessera (the singular of tesserae), it’s important to ensure that it’s suitable for the job and the environment where it’ll be used. 

If you’re in a freeze-thaw area, you should choose tesserae that won’t absorb moisture; stained glass, vitreous tiles or porcelain are good choices. To determine if your tessera is porous, drop some water onto an unglazed area. If the water is absorbed, then the piece is porous. If it beads on the surface, you are pretty right. 

Using a waterproof adhesive and grout will help with longevity. UV light can also cause fading, particularly of crockery or indoor tiles. Be aware that grout may also stain porous tesserae.  

Floors or stepping-stones can become a slipping hazard when using smooth tesserae, especially when wet. Beware of stained glass and flat tile. If possible, select tesserae with a pronounced pattern. Wider grout lines can also help in this regard. 

There’s a huge range of material to use as tesserae and is available from lots of places. Tesserae can include, but are not limited to: 

  • Ceramic or porcelain tiles 
  • Stained glass, mirror, smalti or glass tiles 
  • Crockery 
  • Beads and jewellery 
  • Marble, stone and slate 
  • Rocks and seashells 
  • Hand-made objects – polymer and air-dried clay (indoor only) 
  • Metal objects – bullet shells, paper clips and ball-chain 

Ceramic or Porcelain tiles: Porcelain tiles are made from a fine white clay, fired at a higher temperature than normal ceramic tiles, making them less moisture absorbent. This makes them harder to cut and shape but it also means they’re a much better choice for outside use. Ceramics are easier to cut and shape and are available in a wider range of colours.  

You can find some beautiful patterns on terracotta tiles, however caution is required because terracotta is quite porous and crumbly. 

If you’re using ceramic tiles outside, avoid those with crazing or fine cracks in the glaze. This is an indication that the glaze has been compromised and will allow moisture in. If you think your tiles have crazed, soak the tile in water, then wipe off. Any crazing will show up clearly. 

Crockery: It’s a popular material as it comes in so many different designs. There are different qualities of crockery, and you need to choose wisely (see comments above re cracks in the glazing and ceramic vs. porcelain). 

Beads: They’ve become popular in recent years in mixed media mosaics. Avoid using them outside, as they typically will fade. Cheaper is not always best – there are different coatings on them and some will rub off easier than others, especially when grouting. Discussing your plans with your retailer will mean that they can recommend the most durable option. Some people add beads after grouting – it depends on the job and look you’re after, and the size of the beads. I usually add beads before grouting. I also leave them on a strand as it’s easier, neater and quicker. 

Check out Peter’s YouTube channel Treasury Road for lots more useful tips!

And watch this video for more tips from Peter on tesserae: