Cast Iron Vitreous Enameled Baths

Authors Website: http://www.drummonds-arch.co.uk/

This article describes the original Victorian process for manufacturing cast iron vitreous enamel baths which stood the test of time until the advent of abrasive cleaners in the 1950s. When cleaned properly without abrasives, enamel baths should last indefinitely. Cast iron baths made by Drummonds are made today using these techniques.

Creating a master pattern:

First, a wooden pattern is prepared being the exact shape of the bath but about 8% oversize. This then has spigots attached to the bottom.

The pattern is then pressed into specially prepared casting sand contained in a box. The imprint must be exactly located in the box so that the two imprints (one from the top and the other from the bottom) can be exactly located to create a mould with precise wall and rim thicknesses.

Once this mould has been formed, it is heated up and aluminum is poured into it via the spigots on the bottom. It is then allowed to cool to room temperature and the sand broken away.

This aluminum casting is then fettled and polished to create a master pattern.

This process is repeated, this time using the aluminum master pattern to create the sand mould. Again, the sand mould is heated up and molten iron of a specific analysis is poured into it and allowed to cool down slowly.

Once cold, the sand is broken away and the spigots which formed the fillers are removed. So too are any roughness around the rim.

Quality control:

Throughout this process, strict quality controls are enforced, and inspections made at each stage to ensure a high quality casting. Since it is mainly a manual process, some variations are inevitable and acceptable within given tolerances.

Once the casting has passed its final inspection, it is ready to be transported to the bath enameling plant.

Shot blasting:

After being inspected, a raw bath casting is shot blasted on the inside using a particular size and shape of shot to give a finish that the enamel can bond to, both chemically and mechanically.

Enamel ground coat:

After shot blasting, the cast iron bath is inspected and cleaned before being sprayed with an enamel ground coat. This must be done within two hours of shot blasting.

The ground coat bonds both chemically and mechanically with the iron when hot. The bath is then dried before being fired.

Repeated enameling and firing:

Once dry, a bath is placed in a furnace and heated to about 950°C. It is allowed to soak at this temperature for a short while before being removed from the furnace and sprinkled with dry enamel frit whilst still hot. The bath is then returned to the furnace and brought back up to temperature.

This process is repeated until the bath has had four or five coats of enamel. It is then removed from the furnace and allowed to cool manually.

Once cool, the bath enamel is inspected before being sent to the finishing department to have its feet fitted and appropriate surface treatment to the exterior.

Bath enamel composition:

The composition of the enamel is critical, as the expansion rate of enamel (glass) is much lower than that of iron. A different composition of enamel is needed on the rim compared to the flat parts of the bath to ensure that the enamel remains in compression at all times.

Exterior finishing:

An enameled bath, once it has been inspected and passed, is immediately transferred to the finishing department to have the feet fitted and the exterior treated by either polishing or painting.

Foot fitting:

A bath is inverted on a cradle and the foot lugs drilled and tapped. Feet are then fitted, grinding as necessary to obtain a comfortable fit. Each foot is then numbered with the corresponding lug number. This is to ensure that they are put back in the right location after painting or polishing.

Bath polishing:

If a bath is to be polished, it is transferred to the polishing shop where its feet are removed and lightly shot-blasted before being machine polished.

The bath itself is machine sanded with very coarse emery before the polishing process starts. Bath polishing is a very laborious process consisting of sanding with finer and finer grits to give an even surface.

Once it has been sanded to about 1,000 grit, the bath is polished using a textile buffing wheel to a high shine finish. When a satisfactory shine has been achieved, the bath is cleaned and degreased prior to lacquering.

Two coats of lacquer are sprayed on and baked at a low temperature to ensure a strong bath finish.

The feet are treated with the same lacquer and the bath with its feet is boxed for dispatch.

Bath painting:

If a bath is to be painted, it is transferred to the paint shop where it is machine sanded before the first priming coat is applied.

Following the first primer, any blemishes are filled and sanded before a brushed on filler is applied and sanded to give a smooth finish.

If a bath is being supplied primed and not fully painted, a further coat of primer is applied ready to accept the clients' final painting.

The feet are treated similarly and the bath is then boxed with its feet ready for dispatch.

Metallic paint finish:

If a bath is to have a metallic paint finish, it is treated as a normal paint finish up to and including the final primer.

After the final primer, it is lightly sanded and then sprayed with a metallic paint. After a second coat, the paint is baked dry and two coats of lacquer are applied and similarly baked on.

The feet are treated similarly and the bath is then boxed with its feet ready for dispatch.

© 2005 Drummonds

Editors Note:Drummonds is based in the UK and has built a reputation as a leading supplier of architectural antiques and of period bathrooms since its inception in 1988. Products include a full range of period bathroom fixtures, brass cabinetry hardware, traditional style garden furniture, period lighting for the garden, and fine hand-finished cast iron conservatories.

Note: This article was submitted by a second party and the contents are subject to our disclaimer.