How to clean terracotta pots from limestone

Our terracotta pots from Impruneta are durable and high-quality containers, able to protect plants from the coldest temperatures. However, being made of natural materials, they can undergo aesthetic changes over the time. In fact, you might have noticed a kind of white patina that forms on the surface of the pot. Do not throw away your jar but discover with us instead, how to clean it from limestone.

How to clean terracotta pots from limestone? Here Fornace Masini answers your FAQs

In this article we’ll explain what limestone is, how to remove it and why it is so important to know how to clean terracotta pots from limestone.

What is the white patina that forms on the surface?

The white patina is “saltpeter”, that is a salt, that shows itself as a white mold. In the scientific jargon it is known as “potassium nitrate” and it was used in the past for different purposes: the Romans used it as a natural detergent while the Chinese mixed it with gunpowder to create explosives. Apart from its pyrotechnic uses, today it can also be used as a fertilizer.

How does it form?

Saltpeter proliferates in humid environments and it appears as a superficial efflorescence. The clay of Impruneta turns out to be a fertile environment for its growth because it is rich in mineral salts. It appears as a white patina on the terracotta pots, which is very similar to mold and it usually forms during Winter, as it is more humid.

Why does it form on terracotta pots?

The reasons for the growth of limestone can be the water used to water plants, fertilizers used for the soil or the simple effect of weather over the time on natural materials. This are all reasons why limestone can appear on terracotta vases, but all of them witness the quality of a vase and its craftsmanship. Sometimes the limestone on the pot is a natural phenomenon that can last a few hours and then reabsorbs, other times it can be permanent.

Does limestone damage terracotta pots?

No, it doesn’t: saltpeter does not affect the quality of a pot. In terracotta pots the color is never the same and it can change by many different factors, not depending on the manufacturer.

It can be useful to know, how to clean terracotta pots from limestone for those who want to keep the product aesthetically perfect, but remember limestone doesn’t affect the quality of a vase!

How to clean terracotta pots from limestone?

Often, some water and a laundry brush are efficient enough to remove saltpeter, but sometimes you also need to add a third ingredient: buffered acid.

In this case, here are the 5 steps to learn how to clean the terracotta pots from limestone. Before starting, be sure you wear gloves to avoid acid contact with the skin and wear a mask to avoid breathing any harmful smokes:


  • Empty the pot completely and help yourself with a sponge to eliminate any soil residue on the bottom and edges of the pot
  • Fill a basin with buffered acid
  • Dip a brush in the acid and then, pass it over the entire surface of the pot
  • Brush everything away quickly before the acid is absorbed with a laundry brush
  • Rinse with water and let the pots dry upside down

Do these recommandations on how to clean terracotta pots from limestone always work?

Buffered acid is not always 100% efficient, so if it doesn’t work, try to dilute some muriatic acid with water and repeat the above- described procedure.

Can a pot lose color?

Cleaning terracotta pots from limestone, following our advice, will make your pots have a homogenous color. Despite this, we specify again that handicraft products can always have some aesthetic imperfection, due to the natural material and the craftsmanship, which both attest the authenticity and the quality of the terracotta vases produced in the Masini Furnace.

We hope to resolve any doubts you might have, with this article about limestone that forms on terracotta pots. For this reason, the next time you find the white patina on the surface of a pot, do not worry! Just, follow our simple tips and make your pots turn to their original color!