The difference between Foundry Bronze metal and cold cast Bronze Resin
Whether you are thinking about making a purchase, or about commissioning a bespoke sculpture, it is helpful to know the difference between Foundry Bronze metal and cold cast Bronze Resin in advance. Both materials can be good choices for different reasons.
Foundry Bronze is a metal alloy that is shaped using the traditional method of bronze casting, using the lost wax process – used by sculptors in ancient Greece. The bronze is melted at extremely high temperatures and then poured into a ceramic mould.
The lost wax method of casting is a highly skilled, complex, time-consuming and labour intensive process. Not least because the bronze metal will shrink by up to 5% in the casting. The skill required in the casting, combined with the innate value of the bronze (which is made from copper and tin), gives rise to the comparatively high price of a bronze sculpture.
Foundry Bronze sculpture lasts indefinitely and as the premier and most authentic sculptural material is often considered to be an investment. It is much harder to repair than cold cast bronze if it is damaged, but damage is much less likely due to its strength and durability.
We often recommend a commissioner who comes to us for a bespoke animal sculpture commission choose foundry bronze. The comparative price between Foundry Bronze metal and Bronze Resin is smaller for a commission than it is with a purchase. The commissioner is still paying for the artist’s time and the mouldmaking, whichever material they choose. We certainly always recommend Foundry Bronze for anyone commissioning a public work, or any developer intending to place an artwork outside in a common space. In these instances, it is far more likely that users of the space may unintentionally or intentionally interact with the sculpture in a way that might cause damage. And while Bronze Resin is strong in large sized sculpture, Foundry Bronze metal is far more resistant to knocks and climbing.
Bronze Resin sculpture also known as “cold cast bronze” or bonded bronze, is made of real bronze powder, mixed with polyester, epoxy or another resin and poured into a rubber reusable mould. This is backed up with very strong fiberglass and resin. Because real bronze powder is used over its surface, cold cast bronze can be colored or patinated (a chemical reaction with the metals in bronze) to look very similar to Foundry Bronze.
Other powders other than bronze may be mixed into the polyester or painted onto the surface to enable the resin to achieve the appearance of different materials, such as iron, copper or stone. Casting a cold cast sculpture is faster and less expensive than casting bronze. It is also much lighter and is still relatively strong, as it can be reinforced with an internal steel structure.
Cold cast bronze can last outside for over 35 years, and most last between 50 to 100 years. Depending on the shape some cracking may occur over time, if water pools constantly in one area, some cracking may occur over time, particularly along seam lines if water sits and then freezes.
Indoors bronze resin treated with care can last indefinitely. It is more fragile than foundry bronze and knocking or dropping can break or crack vulnerable parts of the sculpture. However, it is also quite easily repaired and is a fantastic bronze substitute. It’s generally very durable and much more affordable, normally approximately half the cost of Foundry Bronze.
How to tell the difference between Foundry Bronze metal and cold cast Bronze Resin
You may be able to tell whether a sculpture is bronze by the weight, the sound, the temperature, or the colour.
Smaller Foundry Bronze metal sculptures will always be heavier in the hand than a Bronze Resin sculpture would be. It may be harder to tell using weight with larger sculptures, as a large bronze resin sculpture will often be filled (for example with recycled marble dust) to give it substance in the garden and protection against the elements.
The sound is a very reliable way to know whether you are dealing with a Bronze Resin or a Foundry Bronze. A light tap with your ring finger will produce either a metallic sound (Foundry Bronze metal), or a duller more ‘plastic’ sound with the Bronze Resin.
Temperature can also be an indicator, but temperature can be deceptive. Foundry Bronze metal often feels colder to the touch when indoors, or when it is outdoors in cold temperatures. But that does not mean that Foundry Bronze metal is always cool to the touch. Metal is a very good conductor of heat, so a Foundry Bronze sculpture left outside in the hot sun will be extremely hot to the touch!
Telling the difference by eye can often be challenging. The colour of Foundry Bronze metal will usually be deeper and have a greater lustre, particularly in the gold coloured highlights. However, Bronze Resin can look very similar, as with the Standing Retriever sculpture on the left, and it is getting closer all the time! The difference in colour is clearest when you are dealing with a smoother sculpture, with a golder patina, as with the Leaping Dolphin sculpture below.