Etching...Uncovering the Hidden Image. Part 1

The Stages of Chemically
Etching Copper Alloys

This is Part 1 in my series of blog posts on how to chemically Etch Copper Alloys using Toner Transfer Paper (TTP) or Press-n-Peel Blue (PnP, or PnP Blue) sheets as the main Resist. 

There are several metalsmithing techniques to remove surface metal as a form of decoration. The two techniques that often come to mind for me are Etching, a chemical method, and Engraving, a physical method. Both are very old techniques, by comparison Etching methods have changed a great deal compared to Engraving ones. I will not be covering Etching's history in this blog post, but the current methods I practice.

I have been etching mainly Copper Alloys for about 3-4 years, given a few lecture classes at Pennsic, and I've etched several Fine Silver rings which were fun to do. Although the Etchant, the Etching solution that removes the unwanted surface metal, is different for Copper Alloys, compared to Fine or Sterling Silver, everything else is the same in the procedure I follow. I will cover the similarities and differences in a future blog post.

[IMAGE]

The Stages for Chemically Etching Copper Alloys

1. Toner Transfer Paper (TTP) / PnP Blue sheet.

The 'Light Grey' in the image represents the backing material and the 'Blue' is the coated side to be printed on. PnP Blue's backed material is Mylar, a Polyester, it's clear and transparent, which is coated with several layers of release agents so it looks blue. The backing material for TTP is paper with several layers of release agents that look semi-glossy and slightly tinged blue-green. The coated side for both are the sides the graphic images need to be printed on. 

The coated side, represented in Blue in the image, binds the HP B&W Laser Printer's Toner to the sheet and helps during the Heat Transfer process. The Toner is a plastic, not an ink, so it can be transferred onto the metal with heat and pressure / weight.

The Toner used for Brother B&W Laser Printers require a much higher temperature to Heat Transfer the Toner onto the metal. Experiment and see what that is if you already have a Brother brand printer.

2. TTP / PnP Blue with horizontally flipped graphics printed.

The 'Dark Grey' in the image represents the graphic images printed with Toner which acts as the Resist, which blokes the Etchant from corroding the metal. Many/most HP Laser B&W Printers use toner cartridges which use a plastic formula and not an ink. Some of their cartridges have environmentally friendly, 'Green' material, that does NOT act as a Resist and is not useful for etching.

The best images for a cleanly etched design is B&W and NOT Grey Scale. The sharper and smoother the images' edges are the cleaner your etch, so a higher number of Dots Per Inch (DPI) is suggested, at least 300 DPI. Experiment to see the various texture options available to you based on the image used as well as it's DPI, take notes.

The Toner's coverage over the sheet is NOT 100%, due to the method that the Laser Printer covers the paper in Toner and heat treats is to bind to the surface. There are micro sized spaces between the Toner, particles / 'drops', that could allow some Etching solution to get past and create pin holes / pits on the surface of the metal instead of a perfectly smooth surface that was properly protected. Some printer software allow the user to control the percentage of Toner coverage of the paper. If you are able to switch then use the highest coverage available, though this does not guaranty perfect coverage or protection.

3. TTP / PnP Blue during Heat Transfer of Resist onto the Metal.

The 'Yellow' in the image is the flat metal sheet that will be etched, for example, Copper Alloys etched by Ferric Chloride, and Silver Alloys etched by Ferric Nitrate. 

HP B&W Laser Printers' Toner, since it's a plastic and not an ink, can be Heat Transferred onto the metal between 280F to 295F [138C to 146C]. Simply applying heat will not be enough for the Toner to bond to the metal, it also needs pressure / weight and sometimes burnishing the paper against the metal. If the pressure / weight is high enough, during heating, then burnishing might not be needed. If pressure / weight is enough then burnishing the paper is necessary. 

When using a flat heat source that is below the metal and TTP / PnP Blue, for example: an electric cooking grill (sold for making breakfast / brunch usually), large cast iron frying pan, etc. 

I use a rectangular piece of parchment paper, which is sold in rolls and used in baking, as a slip cover / folder during Heat Transferring the resist onto the metal. Cut a piece of parchment paper at least 2 inches wider and longer than the sandwiched TTP / PnP Blue and metal sheet. Once cut fold it in half, place the 'sandwich' in it so that the length of it is firmly wedged against the fold, this keeps everything lined up while you are applying pressure of burnishing the surface.

You can use the back of a metal spoon to apply pressure while burnishing to aid in better transferring the image. Hold the spoon with your thumb in its concave area and while pressing downwards with as much force as you can, burnish / rub the surface in every direction and over 100% of the surface of the metal sheet. Continue the Heat Transfer for approximately 90 to 150 seconds (+ / -), the amount of time will vary depending on the temperature, pressure, etc. used.

Once the time is up carefully remove the bonded 'sandwich' and smoothly slide it into a container of cold water. The backing material of the PnP Blue should slide off within a few seconds on its own. The paper backing of the TTP will take a bit longer and requires to be smoothly slid off by hand. If you see a fine surface coating left over from the release agents, slowly wipe it away with a wet finger, rinse it.

Allow the rinsed metal to air dry completely before taking the next step.

4. Metal with Resist is safe from Etchant, Dark Grey & Orange.

The 'Dark Grey' in the image represents the Resist that is bonded to the surface of the metal. The 'Purple' represents additional resist that can be added: nail polish, tape, etc.. It needs to be applied on the ALL surfaces that you do NOT want to be Etched.

PnP Blue: The emulsion layer on the PnP Blue stays attached / binds with the toner,  even after heat transferring them onto the metal. 

TTP: The emulsion on the paper backing enables the toner to not bond to the papers' surface and more easily slide of during heat transfer.

Please note an unwanted hole in the Resist at the bottom right corner of #4's cross section, it wasn't properly protected with Resist, nail polish (Purple), it is the second type of Resist that was applied. It was coated on every area that shouldn't be etched and it doesn't effect the artwork of the TTP / PnP Blue.

5. Piece in Etching Solution; areas unprotected by Resist will be etched away, the metal being removed is Orange.

The 'Orange' in the image represents the metal that will be chemically etched away, removed, by the Etchant.

Etching Solution = Etchant = Ferric Chloride

When etching Copper Alloys you can use Ferric Chloride, and for Silver Alloys you can use Ferric Nitrate as an Etchant. Both corrosive salts are mild compared to many of the other salts or acids that you can choose to use. Ferric Chloride has been used for many years in the electronics industry and by hobbyists to etched circuit boards, etc.

In the bottom-right corner we see in Orange the tiny area of metal that will be Etched, but should have been properly protected with the second Resist. This unprotected spot will leave a hole or line in the surface of the metal.

6. Etching complete & Etchant neutralized; Resist on surface.

Ferric Chloride is an Etchant for Copper Alloys, and Ferric Nitrate is an Etchant for Silver Alloys, both corrosive salts are neutralized with a Baking Soda solution. If anything that comes into contact with the Etchant, a corrosive salt, and is not completely neutralized, then whatever Etchant remains on it will continue to 'eat' away material. 

To neutralize the Etchant make a solution of tepid/cool water, slowly add Baking Soda while stirring until it will no longer dissolve (disappear). Powder will start to fall to the bottom of your container, super saturation, this is a good way to be sure that you are using enough Baking Soda. When the Etchant comes into contact with the neutralizing solution you will know that it is working when frothy bubbled start to form. Once those bubbles stop forming, similar to when popcorn pops slower and slower until it stops, all the Etchant on the surface has been neutralized. While wearing latex or neoprene??? gloves you can gently rub the surface to expose more surface area then return into the Baking Soda solution. Remove the piece then place it into a fresh batch of Baking Soda solution, this 'clean' solution will get into any areas that weren't neutralized earlier. Remove and rinse in a container of tepid water and leave to air dry.

The hole at the bottom-right corner is more visible after the piece was Etched. 

When I remove my pieces from the Etchant:

1. Before putting anything into the solution of Baking Soda, stir it to be sure it's mixed in enough since it quickly separates. 
2. Pat everything dry with paper towels to remove as much moisture as possible from the piece and floater.
3. Submerge everything into the Baking Soda solution. You'll know it is working when frothy bubbled start to form, keep the piece in the solution until the bubbles stop forming.
4. Remove the metal from the first container of neutralizing solution and put it into a fresh container filled with neutralizing Baking Soda solution. Once the bubbles stop forming remove the piece and rinse it well under tepid water. Pat dry and leave everything to air dry.
5. If you used any tape you should remove it now, continue letting it dry.
6. Acetone, nail polish remover, will remove the TTP / PnP Blue, nail polish, and some of the tape residue. 
7. Use some dish soap to wash the piece and rinse it well under tepid water. Pat dry and leave it to air dry before continuing.

7. Etched Piece once the Resist is removed.

Now it is ready for you to work with it, you can: saw, pierce, file, sand, drill, solder, polish, etc. to complete the piece.

Safety Precautions:

Always keep a container with fresh Baking Soda solution nearby as well as an open box of Baking Soda when dealing with Etchant. Wear safety glasses, gloves, clothing that covers as much skin as possible, and close toe shoes. Keep hair tied up and out of your way. Work in a well ventilated room if you cannot work outside. Having a stove top fan on while working under it is good as well. Cover all your work surfaces with newspaper or plastic. The Etchants can stain everything it comes into contact and possibly corrode.


TO GO TO PART 2