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Photo etching is a complicated process that involves some impressive machinery and a whole host of different chemical solutions. From the pre-process cleaning and prep to washing the metal after it has been etched, there is a very specific system in place, with chemical cocktails and a selection of associated machinery that requires precision and skill.

As interesting as the overall process is though, it is the different chemical and wash solutions that are the most demanding and intriguing part. The way they work, the accuracy of each solution on a job by job basis, and the knowledge of chemistry necessary is fascinating.

In fact, the selection of chemicals used in the different stages of the photo etching process could be mistaken for an industrial cocktail menu.

To give you some idea of the different chemicals and chemical cocktails we use here at Qualitetch, as well as what each one does in this process and in its other uses, read our Photo Chemical Cocktail Menu, below.

Phosphoric Acid

Cleaning solution; to degrease metal pre-process

The first chemical on the menu, phosphoric acid, is used to clean and prep the metal surface, so it is grease and oil free for the photoresist laminate to adhere. The cocktail recipe includes phosphoric acid (30%), degreasing agents and water is added to dilute the solution. The cocktail is then used as part of the heating-soaking-rinsing process to clean the metal sheets. Interestingly, phosphoric acid is also used in skincare products, leather treatments and Coca-Cola.

Photoresist Polymers

Dry film photoresists

There are two main types of photoresist; wet film resists where the metal sheets are dipped in liquid resist and dry resist which is applied by laminating rollers. Dry resist is actually a polymer film which is fixed to the metal surface when exposed to UV light. This polymer film is versatile in purpose and industry, also being used for medical and 3D imaging processes.

Ferric Chloride

Photochemical; the main etchant

Ferric chloride is the most commonly used, and most readily available, photo etchant. It is versatile, making it suitable for use on any number of metals and alloys. It is a black solid that dissolves in water and creates a reddish-brown solution. As well as photo etching, it is also used in water purification and treatment, in the production of indigo blue dye, and by veterinary practices that need to stop animals’ paws bleeding when they’re over-cropped.

Ferric Nitrate

Photochemical; the etchant for silver and other specialist metals

Used less often, ferric nitrate is the etchant of choice for non-standard etching. It is usually used on materials like silver and molybdenum. As well as being used in photo etching for large-scale projects, it is also used by jewellers, metalsmiths and artists who need to etch silver and silver alloys for decorative purposes.

Caustic Soda

Sodium Hydroxide; used to remove the photoresist

Caustic soda, or sodium hydroxide as it is scientifically known, is used as the final wash for photo etched metal. As a rule, different chemicals are used to clean different resists. A mild caustic soda solution, like the one on our photo chemical cocktail menu, is most commonly used to remove dry film resist though. It is also used in cleaning agents and food and water preparation, as well as in various chemical and industrial settings.

So there you have a brief guide to the chemicals and solutions on our Photo Chemical Cocktail Menu. Of course, the substances discussed have other uses, but they each play a significant role in our photo etching process, so it is good to know a little more about them.

Now you know the chemicals though, why not get in touch and find out more about what Qualitetch do. We are always happy to discuss your ideas, our projects and our capabilities. Alternatively, see the rest of our website for more information on our services.