It is easy to feel nervous when you read some of the information about caustic soda. It is potentially dangerous, but then so is a craft knife, that’s why it is important to understand its properties and manage your use of it safely.

What is caustic soda?

caustic soda bottle

Caustic soda bottle

Caustic soda it comes as a coarse white powder that forms a strong alkali when you add it to water.
The chemical is Sodium hydroxide, NaOH.
It is most commonly used in domestic settings for unblocking drains, although there are many industrial and food uses as well.

Properties of caustic soda

Caustic soda decomposes proteins. Proteins are things that are (or have been) alive – for example plant and animal tissues, so natural oils and fats, hair, and skin. This also includes you!

If you get it on your skin it will cause painful chemical burns.

It does not affect man made materials (but can affect aluminium,) so use plastic containers to mix it in, rubber gloves and plastic aprons, tablecloths etc.

Where can you get it?

Your local hardware store or diy depot will supply it as a drain cleaner. Keep it in the original container and label any mixed up caustic soda clearly.

Mixing caustic soda

apron, gloves and goggles

protective gear made from synthetic materials

You can mix up caustic solutions of different strengths depending on what you are using it for.

Pour water into a plastic container and always add the powder to water, never the other way round. (There is a danger of the mixture ‘exploding’ and splashing).

There is a chemical reaction; it becomes hot and gives off fumes for about 30 seconds after mixing – take great care at this stage.

Use rubber gloves that cover your wrists, and wear goggles in a well ventilated area when mixing it up.

If you get it on your skin wash it off with plenty of water for 10 – 15 minutes.

Read the safety instructions on the container before using caustic soda.

If this all sounds rather dangerous, don’t be scared – just be sensible and make sure you are well prepared.

A little bit of history….

manuscript illustration of a medieval bath

medieval soap made from lye

Since the early middle ages Sodium Hydroxide has been made by burning sodium rich plants, then straining water through the ashes. The liquid is known as lye or soda ash and is used with natural oils or goose fat for soap making.

You could try this if you want to be truly self sufficient.….

How do printmakers use it?

There are a couple of ways that caustic soda is particularly useful in printmaking;

  1. Lino etching

Traditional lino is made from linseed oil and chalk – linseed oil is a natural protein so the caustic soda will dissolve it.

If you try it on vinyl based ‘soft cut’ lino it will have no effect as this is synthetic and doesn’t contain proteins. Have a look at the ‘lino etching’ post to see how to do it.

  1. Papermaking

To make paper from plants the soft tissues need to be separated from the stronger fibres, caustic soda will do this for you.

Be adventurous!

Caustic soda is a powerful chemical that works really well for etching lino. Like many useful substances it also comes with dangers, but if you plan your work space, understand the risks, and use it carefully it will enable you to create beautiful textured lino plates.