Dish washers and glass

[Dave]

I have just come from another ng and the subject was 'pyrex' and dishwasher powder. Can anyone tell me how borosilicate glass is affected by DW powder?

Dave

[Stewart]

They go cloudy

[Stewart]

They go cloudy

[Andrew Gabriel]

Pyrex is a name licenced out to a number of companies around the world, and they make their products from different types of glass, so I wouldn't assume Pyrex just means one type of glass. I have both UK and US pyrex (which are different glass), and neither has ever suffered damage in the dishwasher. (Some drinking glasses have.)

[S Viemeister]

I have US-made Pyrex, and have washed it in my UK dishwasher, with no ill effects. I have a few pieces of US Pyrex which have been washed in my US dishwasher (Grab-It lids), and they have gone cloudy, as did one old measuring jug. None of my other Pyrex, whether US or UK, has done this, either using US machines and detergents, or UK ones..

[Andrew Gabriel]

There are two mechanisms for going cloudy. They look similar in effect, but are very different. One is a surface contamination, which can be removed with a mild acid (such as vinegar). The other is a leaching inside the glass itself, and this tends to happen in glass roughly in proportion to the lead content (and probably detergent concentration/exposure), so don't clean your lead crystal glasses in a dishwasher. Lots of glass which you might not regard as lead crystal has lead in it, but like I said in another post, I've never seen this happen with Pyrex.

[John]

As an off shoot to this thread. My local recycling centre (used to be a Council Tip) says "No Pyrex" in the glass bins. Why is this? The local ever so helpful (not) waste management operative said "I haven't got a clue mate".

Cheers

John

[Rod]

This was asked the other week. I suggested (having seen a program showing production of glass fibre from waste glass) that it might be to do with the temperature required to melt it being considerably higher than 'normal' glass. Hence, the standard process cannot handle it.

[John Weston]

I asked via the phone number on our recycling list some time ago and was told they exclude certain categories of glass due to additions in their manufacturing process - such as lead in crystal glass. etc. Don't know if this as the problem with Pyrex but...

They also exclude window glass, but this is probably because the likely- to-be-broken pieces cause problems for the equipment they use to separate it - or the manual sorters.

[D.M. Procida]

I read that a single Pyrex item can render a whole load of glass unreclyclable.

Daniele

[Chris Hogg]

Most container glass (bottles, jam-jars etc) and window glass is soda-lime-silica glass, essentially made from soda ash, limestone and quartz sand melted together, with one or two minor additions. It has a relatively high coefficient of thermal expansion, which means it cracks if heated suddenly. Pyrex type glass has a much lower expansion coefficient because it contains much less soda and quite a lot of boric oxide (B2O3). If Pyrex gets into a batch of container glass, the high B2O3 content changes its melting and moulding behaviour and the bottle-making machines can't cope.

I'm not sure why window glass is also excluded from bottle banks. AIUI, its pretty much the same composition, but there may be subtle differences. Alternatively, as John Weston says, it may just be because bottle shapes are easier to handle by sorting machinery etc. than flat panes and large shards.

Lead crystal glass has a different composition again. Less soda, much less lime, but with additional potassium and lead oxides. While the lead oxide gives the glass a high refractive index and sparkle, it also makes the glass more prone to being etched by alkali such as in a dishwasher, and going cloudy.

[Andy Dingley]

How much recycled glass goes for bottle making, and how much is just headed for glassphalt though?

[Chris Hogg]

Not got a clue, but if it all goes for glassphalt, I don't see why Pyrex would be excluded. But even if only a small proportion is recycled for bottles, you wouldn't want a high-B2O3 glass in it.

[Huge]

According to what I've seen and heard, it all goes for glassfibre insulation anyway.

[Steve Firth]

Mindboggling quantities go for use in roadbuilding. I was told that there's a huge imbalance in the quantities of glass received and the quantities required. The UK demand is for brown and clear glass, which makes up a minority of recycled glass. Most recycled glass is green, wine bottles and one-way beer bottles.

Come to think of it, I've not seen much green glassfibre insulation.

Anyway, I'm happy for it to end up in the roads. It seems as good a use for it as any.