Porcelain or Enamel dials?

[Tom McIntyre]

It seems to be common practice with clocks to refer to the dials as porcelain. Is this term used to refer to ceramic dials fired in a kiln with applied decoration?

When powdered glass is fired onto a metal substrate the result is called enamel rather than porcelain. It is my impression that most glazed clock dials are made of enamel rather than porcelain.

I cannot find any porcelain dials on my clocks. Most are painted metal, but several of the smaller ones and most of my pocket watches have enamel dials.

Here are the examples I have out for display.

 

[Tom McIntyre]

 

[tracerjack]

I am inclined to agree with you that technically they are enamel dials, not porcelain, but I am not an expert, so just my opinion. Calling them porcelain makes me wonder if it was to make them sound better for advertising. Porcelain would have association with high quality items. Hopefully, someone with historical knowledge can answer that question.

 

[T.Cu]

Tom, I have also heard the fired copper or other metal substrate with glass melting onto it dials are correctly called "enamel", not "porcelain", as you describe. My source maintains "porcelain" would have to be true porcelain, like a fired clay substance. I am interested to hear what others say.

 

[Mike Phelan]

I've also seen dials on the forum referred as porcelain that are actually enamel (glass) and thought this was just a USA vs UK thing.

Porcelain is melted china clay and first came from China.

 

[Tom McIntyre]

As a counter note, bathtubs with something, I presume clay, fired onto cast iron are called porcelain. Does anyone know how those are made?

 

[tracerjack]

Here is my guess. ‘Enamel’ also goes by the term ‘porcelain enamel’, defined as a glassy coating fired onto glass or metal, Porcelain Enamel
Most likely, the term ‘porcelain enamel’ was shortened to just ‘porcelain’ assuming others were familiar with the correct full name.

 

[wisty]

As a counter note, bathtubs with something, I presume clay, fired onto cast iron are called porcelain. Does anyone know how those are made?

I think they are more correctly called "vitreous enamel". The matching handbasins and toilet pans are probably made of pottery - possibly porcelain. At which point marketing takes over!

 

[demoman3955]

enamel is closer to correct, because its a glass and porcelain is a clay, but im bad at using the incorrect term and mixing the 2

 

[T.Cu]

I think "vitreous enamel" is a keeper for me. Makes it sound less like enamel paint.

 

[Mike Phelan]

Just for interest:
The European name, porcelain in English, comes from the old Italian porcellana (cowrie shell) because of its resemblance to the surface of the shell.

 

[Tom McIntyre]

Just for interest:
The European name, porcelain in English, comes from the old Italian porcellana (cowrie shell) because of its resemblance to the surface of the shell.

That is interesting and brings us to the name used for the shell when used in watches being called mother of pearl.

 

[tracerjack]

I’m sticking with the full name ‘porcelain enamel’, since that is an official name for the process.

 

[tracerjack]

A little further digging - the process called ‘porcelain enamel’ is also called ‘vitreous enamel’. So the bathtub and clock dials are produced by the same process.

 

[Tom McIntyre]

Is it the same process? I did not think there was any clay in the clock dials, but I could be wrong. I know there is no clay in watch dials. The material applied to the metal base is all glass, which is called enamel when fired on to the dial.

Since it is common to use the name enamel for paint processes, some users may prefer porcelain to enamel because it sounds more valuable. Of course it really could be porcelain or porcelain enamel on clocks, but porcelain is definitely clay based.

Are there examples of glass being fired on to a porcelain clay substrate? I think that in pottery the decorative material is also a colored clay.

 

[Tom McIntyre]

Are there examples of glass being fired on to a porcelain clay substrate? I think that in pottery the decorative material is also a colored clay.

In looking for the answer to this subquestion I found that enamel (glass) is used in decorating fired clay objects.

This site is a little ad heavy but seems to provide a good answer Enamel vs Porcelain - What's the difference?

 

[gmorse]

Hi Tom,

Is it the same process? I did not think there was any clay in the clock dials, but I could be wrong. I know there is no clay in watch dials. The material applied to the metal base is all glass, which is called enamel when fired on to the dial.

Since it is common to use the name enamel for paint processes, some users may prefer porcelain to enamel because it sounds more valuable. Of course it really could be porcelain or porcelain enamel on clocks, but porcelain is definitely clay based.

Are there examples of glass being fired on to a porcelain clay substrate? I think that in pottery the decorative material is also a colored clay.

I'm clear in my own mind, (and I believe in those of most UK horologists'), that the vast majority of these dials on clocks and watches are made by fusing various glass powders onto a metal substrate, most commonly copper but gold on the very best quality work. The term 'enamel' is entirely appropriate for these dials. There's always a balancing enamel coat on the reverse of these dials, so the metal substrate isn't immediately apparent.

The temperatures necessary to fire true 'hard-paste' porcelain, at around 1305º-1346ºC, are higher than the melting points of copper, 1084ºC, and gold, 1063ºC, so a china clay coating on a metal base would be impractical. Porcelain dials are known on watches, mostly on very early pieces, but those are relatively rare. The ingredients of porcelain vary, but are mainly feldspar, quartz and china clay, ('kaolin'), in varying proportions.

The gloss surface on ceramic objects such as sanitary ware is, I believe, a glass-based glaze.

Of course, enamels aren't necessarily opaque, see guilloché.

Regards,

Graham

 

[novicetimekeeper]

There is enamel paint, stove enamel, and vitreous enamel. Baths, clock dials, cookware, cooking stoves, these are all coated in vitreous enamel.

There is no clay involved as far as I'm aware.

 

[tracerjack]

While there is no porcelain clay involved in dials, the process of melting glass to a metal base is correctly termed “porcelain enamel” and also “vitreous enamel”. Calling a clock dial “porcelain” is only confusing if one did not know the full term is “ porcelain enamel”.

 

[gmorse]

I wonder if we're experiencing a difference in horological usage between the two sides of the Atlantic?

 

[Mike Phelan]

Quite possible, as The word European name, porcelain in English, comes from the old Italian porcellana (cowrie shell) because of its resemblance to the surface of the shell.
It would melt copper!
As others said, enamel is just glass usually fused to opaque white on a dial.

 

[tracerjack]

“Porcelain”, the fine ceramic that is made of a specific type of clay simply shares a same word as “porcelain enamel” which is an entirely different process. The two manufacturing processes have nothing in common aside from the word “porcelain”. I imagine the term was borrowed for the enamel process since white enamel has a similar appearance to white porcelain china. It is correct to call a clock dial “porcelain” from the process “porcelain enamel” and to do so does not mean it has clay in it.