Perspectives on greener product development and manufacturing from Sustainable Minds, our partners, customers and contributors.

Glass or Ceramic?

By Travis Lee on November 6, 2009

One of our designers here at LUNAR was recently working on a project that required a material with a cold, smooth, high-quality feel, and she asked me which was a more sustainable material, ceramic or glass. This is what I told her:

Glass: There are many different types of glass, but I’ll focus on soda-lime glass here, the type most commonly used in containers, windows, etc. Glass is heavy and often gets a bad rap for that, but if recycled properly it is one of the few infinitely recyclable materials in common use today. It is also one of the few materials with a well-developed recycling infrastructure in almost every developed country. It can be fragile, but can also be made to be durable with various geometries and wall thicknesses (think about how long old Coke bottles stay in circulation). Glass can be considered, for all intents and purposes, to be non-reactive, so it won’t off-gas or leach like plastics.

There are some pretty destructive practices involved in mining basic ingredients for the mass production of glass, but if the product is made from recycled glass, that is not a concern. There is also an issue with the extreme longevity of glass. You’ll see quoted here and there that it takes a million years for glass to completely biodegrade, but the actual time is much longer than that. The bottom line is that once we take minerals from the earth’s crust and transform them into glass, they’re basically glass forever. This is another reason that using recycled glass is very important.

The glass we have already created is not going anywhere, so we should make something out of it in order to reclaim this “technical nutrient”.

So the bottom line is that recycled glass is a good choice for a product that won’t be transported much, is not subjected to high impact, and is sold in a region that has recycling facilities.

Ceramics: There are many different types of ceramics, but I’ll just speak to clay-based ceramics here, which are commonly used for flatware, mugs, vases, etc. Ceramics have most of the downfalls of glass, but lack one of the most important upsides: ceramics cannot be recycled. They can be down-cycled, which involves grinding them up and dispersing the power into a slurry used to create other ceramics, but the resultant product is usually weaker than the original.

Glazed ceramics have the same chemical stability of glass (glaze is essentially, although not exactly, a thin glass coating over the ceramic). Ceramic also has the same extreme longevity issue as glass, which is why we keep digging up ceramic garbage that people tossed out four or five thousand years ago.

Ceramic is lighter than glass, but usually because it is porous. This means that to make products equally durable, you have to make them thicker so they often weigh about the same (compare a drinking glass to a coffee mug). One of the big benefits of ceramic over class is that ceramic is a good thermal insulator due to its porosity. It’s also very good with extreme changes in temperature (glass will break if the temperature on one of its surfaces changes much faster than the other).

So, ceramics are a good choice for an application that requires extreme longevity, good insulation, or excellent resistance to changes in temperature, but if you’re going for a cold, smooth, hard, high quality feel, I’d stick with glass.

Comments

Posted by Travis Lee on Nov 25, 2009

Thanks for the comment, phillyphil. You’re absolutely correct that much of the world’s glass does not get recycled, but it’s important to note that in this case I’m advocating the product in question be made from recycled glass. This option is not available with ceramics and sourcing recycled glass for more products can bolster the glass recycling infrastructure and the value of that quality of glass in the market.

I also agree with you that in any major materials choice there should be a complete LCA done when possible. Without adequate schedule or budget, however, and in the early stages of the product design cycle when the materials suppliers, manufacturers and sales locations have not been specified, this type of full blown analysis becomes difficult. I think this is a good example of an instance where it helps to step back and look at the choice on a much more macro level. On that level, the use of a recycled material and the potential for that material to be recycled (especially if you have control over a take-back infrastructure) usually trump all other factors from a carbon footprint perspective.

Posted by phillyphil on Nov 19, 2009

Realize that most glass is not recycled due to its absence of economic value in the recycling market. This is due mostly to the difficulty in obtaining a pure enough stream (color, type, etc.) to make new glass. However, a growing practice for glass is to downcycle it into a construction material - as an aggregate for asphalt and concrete and as a drainage material for construction (e.g., pipe bedding). If you consider this, then ceramics may not be as disadvantaged in this comparison. I would look more at the carbon and materials footprint of each to compare adequately. Since ceramics may contain higher concentrations of metals, they may have a higher materials footprint. Also, I would think that glass could be made in more of a continuous manufacturing process vs. ceramics where the base is fired and then glaze applied and then refired which could lead to higher energy consumption. I haven't done a formal LCA on this but it seems that this article misses some key points of an LCA comparing the two - namely resource extraction and energy/carbon footprint.

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