Why should we use unleaded glaze for pottery?

A presentation to the UK pottery industry March 3rd 1992 by I.Wozniak

Why use Unleaded glaze and colour in pottery?

In the next 20 minutes I intend to relate some of the background and history to the current lead issues and explain why ‘unleaded’ is the only way forward for the pottery industry.

I am sure you are all familiar, by now; with the story of the Wallace family of the USA who suffered acute lead poisoning from poorly formulated and fired lead glazed pottery bought in Italy. The story is an interesting one but is nothing compared to what followed. The Wallace case has catalysed the beginnings of a revolution in the tableware industry which is leading to the introduction of unleaded systems.

But do we really have a problem with lead? Does scientific reasoning and fact support the argument that lead should be banned from further use in ceramic tableware? Or is it all political hype?

After all we have been eating and drinking from ceramic wares all of our lives and we are not suffering from lead poisoning. Or can some of our past malaises have been due to ingestion of excessive quantities of lead without knowing it? Lead has long been known to be a toxic substance. Indeed ancient Egyptians used lead for homicidal purposes.

History

It is worth looking at the history of the use of lead in pottery. Lead compounds have been used in glazes since Pre-Roman Times. Their properties of easy fusibility, high gloss and relative abundance, 13 ppm in the earth’s crust, together with their glass forming ability have made them an essential ingredient in almost all glazes.

Lead release from ceramic ware was not recognised as a problem until the 1750’s when harvest workers were poisoned by drinking cider from lead glazed pots. Indeed the famous Josiah Wedgwood knowing that lead glazes were ‘improper for preserving acid fruits and pickles declared “I will try to make a glaze without lead”.

In 1896, lead poisoning became a notifiable illness and 432 cases were reported of which most were lead workers.

In 1898 as a consequence of the number of cases of lead poisoning reported, the government appointed an eminent Professor, Professor Thorpe, to investigate the feasibility of substituting leadless glaze for those containing white or red lead. Instead of leadless glazes he came up with the idea of melting the lead compounds with other materials such as silica to form a glass ‘frit’ or ‘flux’. These were much safer to use than the previous raw lead compounds since they were less soluble in stomach acids. By 1913 lead frits and fluxes were commonly used to make glazes and colours.

In 1947 the government introduced sufficient penalties on the remaining users of raw lead oxides in glazes and colours to effectively ban their future use.

Terminology

It is worth explaining a this point some of the terminology used in pottery industry regulations:

Lead release is a term used for the release of lead from fired ware when subjected to acid

Lead solubility is a term used for the solubility of glaze or colour powders in stomach acids prior to firing.

Lead content is the percentage lead content in the unfired state and has no relationship with ‘lead solubility’ or ‘lead release’.

Lead release legislation

In 1968, Finland introduced strict legislation on metal release from tableware. The limits imposed, a total of 0.6mg per dm of area of total lead, cadmium, antimony and zinc, caught the UK industry unawares and a shipment of ware was stopped by the Finnish customs.

In 1972 the UK introduced legislation governing lead release from tableware (BS4860).

About this time glaze and colour manufacturers worked hard to develop lower and lower metal release glazes and colours. By 1982 very low metal release, low solubility colours were available, as well as the first range of unleaded colours.

Nevertheless it was not until the dramatic proposals of the FDA to reduce lead release limits for pitchers in 1989 that the tableware industry seriously considered the use of unleaded glazes and colours. These proposals required that Lead release for pitchers should be reduced 25 fold from a maximum of 2.5 ppm to 0.l ppm. Such limits could not consistently be achieved by manufacturers using lead glazes and colours and an international committee was set up in America to resist to FDA proposals. The committee known as the ‘Coalition for Safe Ceramics was supported by the UK tableware manufacturers and was successful in that the level finally introduced for pitchers in 1991 was only 0.5ppm, a five fold reduction.

Although alarmingly low, UK manufacturers believe they can meet these new lead release limits for pitchers.

The FDA, at the same time as issuing the ruling on pitchers, issued new limits for other tableware including flatware. Here again much reduced limits were imposed. For cups and mugs the limit was 2.0 ppm. The flatware limit was set at 3.0 ppm.

If we look at the FDA trend since lead release limits were introduced over 20 years ago, the reductions in lead release have been dramatic For example limits for cups and mugs have been reduced from 7 ppm to 0.5 ppm. If the trend continues at this rate, by the year 2000 the levels would be less than 0.l ppm. But more considerations were to follow the FDA ruling in 1991. The state of California decided to introduce their legislation governing lead exposure. Proposition 65 rules that, with respect to lead, any article which exposes a consumer to more than 0.5 micrograms of lead per day must be identified at the point of sale by a warning notice. The notice is required to indicate that the product will exposes a person to lead and that lead is ‘a chemical known to cause birth defects or reproductive harm’. To be below the lead exposure limit, tableware manufacturers must be able to conform to the limits:

For Flatware .226 ppm

For Small Holloware .023 ppm

For holloware used for cooking & storage .006 ppm

For others .023 ppm

Because of the uncertainty of the accuracy of measurement to such low levels, a temporary limit of 0.l ppm is currently being imposed. These limits can only be met by the use of unleaded systems.

Packaging legislation

CONEG is yet another lead issue in the USA. This multistate legislation is concerned with limiting the lead, cadmium and mercury and hexavalent chrome content of packaging materials to very low levels to protect the environment.

For example whisky flagon glazes are required to have a lead content less than 600 ppm. Progressive reductions to 250 ppm in 1993 and then to 100 ppm after 1994 will be necessary.

It is also quite likely that, in the not too distant future, this regulation will become federal regulations. EEC regulations are already in the drafting stage and will no doubt be similar.

It is worth considering at this point some of the medical aspects of lead exposure and subsequent result in the body. Lead exposure, for example from lead in food or drink, will result in intake into the body. A proportion of this intake is taken into the bloodstream as uptake. The uptake can be cumulative and lead to toxic effects. Although various scientific models have been put forward relating intake of lead to uptake, there is currently no reliable scientific model.

It is therefore very difficult to set safe limits on exposure to lead. Nevertheless legislative bodies are making decisions based on intake rather than uptake of lead. As usual the limits are set first and scientific evidence considered later.

But what about lead issues closer to home?

The UK will, no doubt, be guided by the EEC directives on lead release. These UK lead release limits are constantly under review and it is highly likely that they will be reduced further in coming years.

Environmental pressures

Other environmental pressures are also growing in force. The cost of improved

controls to reduce or stop lead release into the atmosphere, or into effluent will become excessive over the next decade. Similarly the cost of disposal of lead waste will become prohibitive.

Political pressures and financial pressures from company shareholders will continue to force industrial companies to look for and provide more environmentally friendly products and processes.

But more importantly, the market place is already demanding more environmentally friendly unleaded products.

And so, to answer the question “Why Unleaded? “

Because political, environmental and commercial forces are driving the market away from lead based products. Scientific evidence and reasoning cannot stop this movement.

I am in no doubt that the way forward is with unleaded glazes and colours.

You should be in no doubt that it is the only way forward for the tableware industry!

Lead testing

It is worth noting that leaching of heavy metals such as lead from the surface of a fired glaze is influenced by by the composition, the stain or colouring oxide used, and the firing process. Copper oxide for example should be avoided in lead glazes intended for food use. Similarly any glazed surface intended for contact with foodstuffs should be tested for leaching by an approved test centre! However quick tests are available as a guide to the potential problems.

Lead test kits-quick test for pottery items

Test Your Pottery for Lead using Lead Inspector Lead Test Kits!

Click here to learn more about a lead test kit!