This article will take an in-depth look at acid etching.
The article will bring more detail on topics such as:
This chapter will discuss what acid etching is, its uses, components, and procedure.
Acid etching, also known as chemical etching or photo etching, is the process of cutting a hard surface like metal by means of a specially formulated acid for the process of etching in order to allow for the creation of a design onto the metal.
The process of acid etching is an ancient and reliable industrial process that utilizes different commonly available mordant acids together with chemical compounds to impart an aesthetic or physical improvement to the surface of a metal.
The process of acid etching is a sheet metalworking technology that utilizes acid etchants for the machining of complex, highly accurate precision metal components. Acid etching is used to reproduce works of art with high quality. Initially, the process of acid etching was used to get the work of an artist into the hands of as many people as possible.
The engraver takes a plate of copper or mild steel. The artist covers the entire surface of the plate with a waxy substance that is referred to as ground. This substance is resistant to the acids that are selected to be used. Using a variety of tools, the engraver will then reproduce the original work of art by engraving the image into the waxy ground. There will be submerging the plate in a bath containing the mordant. After a prescribed time, the plate is removed, rinsed off and the ground is removed. This will leave an image that will be an exact copy of the engraver’s work. This process is a very skilled one; it takes time and money to use this way of producing works of art.
The types of materials on which the process of acid etching works equally well are stainless steel profiles, sheets and plates and other metals like aluminum and brass. These types of metals are suitable for the process of acid etching. The surface of stainless steel that is left is usually matte in nature and will be different in texture from the part of the unetched stainless steel. This means that the process of acid etching is used to produce a grip that is non-slip to the stainless steel surface, making hand tools safer. Acid etching is also used to create patterns that are used for decoration, contrasting surfaces, or text.
There are various types of acids that can be utilized in the etching of steel and stainless steel including nitric acid, hydrochloric acid or sulphuric acid. All of these acids require careful handling; therefore caution must be taken when handling them. These acids are capable of dissolving stainless steel as well as fingers.
Chemicals that form acid when mixed with water, like ferric (iron) chloride or copper sulfate can also be utilized as etching chemicals. These compounds of chemicals work faster than acids. The rate at which the steel will be etched is generally determined by the acid’s strength.
The stronger the acid, the faster the etching process. Etching acids and chemical compounds can be obtained from online chemical supply stores.
The type of metal that is etched affects the acid etching process since so do the metals etch quicker than others. Steels and nickel take much more time to etch than softer metals like bronze, copper, and aluminum.
Any metal can be acid etched with attractive metals being the most popular ones because of their properties and characteristics. Metals that are commonly used in acid etching are shown below:
This chapter will discuss the different types of acid etching on different metals. It will also discuss examples of procedures taken in executing the different types of acid etching.
The following procedure was followed during the process of acid etching a steel folding knife.
The most important step in this whole process is preparation. If there is no proper preparation, the results will be poor and also frustrating.
No acid must get on the scales, washers, or liners. Store all the little screws in a safe container or magnetic tray. If you don’t feel comfortable with taking the knife apart, then make sure that you mask off any part of the knife that you would not like to get the acid on.
This is done to provide a clean surface for the etch resist to adhere to. Avoid touching the blade with bare hands after finishing the cleaning process. The oil coming from your fingers together with the etch will mess.
Create a pattern on the steel by using anything that you can imagine. The basic idea is the creation of a barrier that prevents the acid from reaching the steel. This will leave a pattern after the removal of the etch res/istance. Every part of the metal that is exposed will be darkened and also marked by the acid.
You can experiment with sharpie markers, nail polish, vinyl, electrical tape, stickers, and different stenciling materials. If you need to black out the whole blade, then use very little etch resist. Only the pivot and lock face. If you need only a little logo then you must protect most parts of the blade with tape or even nail polish. If you are using the process of etching on a folding knife, then you will want to protect the detent, pivot, and lock face area. You wouldn’t want to mess with the tolerances of those areas.
If caution is not taken, too much metal can be eaten away and totally ruin the knife. Using a bright color nail polish helps by making it clear to see where it has been applied. If you are using the process of etching on liners and scales then you would want to protect the ball detent and the same pivot area.
Before mixing the etch acid you must put on your gloves first. Mix the ferric chloride with distilled water in a ratio of one to one. There is no need to go full strength to obtain results. Pour a quantity of water into your plastic container, and then add the same quantity of acid into the container.
A bit of space must be left when filling the container to allow for the displacement of the blade. The best practice is always adding acid to water to avoid dramatic chemical reactions or splashed acid. Using a container with a better lid is important, especially some sort of Snap-on lid.
If you use the screw lid, it will get messed up by the dried acid crap when it gets in the threads. Do not mix the acid and the water in a metal container because the acid will eat through the metal. This mixture lasts for a long time but it depends on the type of metal that you are etching and how much material you want to strip away.
Before you start etching, always make sure that you are in a ventilated area. There will be a vapor by-product from the reaction since the acid will cause a chemical reaction. This must be done outside or under a vent/stove hood.
The two processes of acid etching are explained below:
It has been found that short dips together with quick rinses under the tap gives the best results. To dip the knife into the acid, you can make use of a paper clip or dental floss. Repeat the same process until the desired results are obtained. Short dips help by providing better control over the end result.
This process will also preserve any of the laser factory markings that are on the blade. The recommended timeline is 10 to 60 seconds bath, 10 seconds in the air, rinsing under the tap, 10 seconds in the air, then repeat the same procedure. It is also recommended to move the blade around in the acid. There are also sophisticated systems with fish tank aerators that can bubble and also agitate the acid.
The movement helps by ensuring a consistent etch with less pitting. Others only do one long bath in the acid. This eats away the metal and makes it difficult to see when enough has been reached. Recommended length is 10 minutes of a bath. Caution must be taken on fingerprints. Try not to touch the blade with your bare hands when rinsing it, as this may leave a fingerprint mark on the blade’s surface.
This works better when you want to put a small mark on the blade or when you are only marking one side of the steel. Ensure that the blade is tapped off using electrical tape, nail polish or vinyl to protect the steel. You can make use of a cotton Q-tip for the soaking up of a bit of acid.
Apply the acid to the steel that is in the stencil. Use the same timeline as before or you can feel with the Q-tip for when the acid begins to bite the steel. The Q-tip must be rubbed around the stencil, working the acid into the steel. The tip of the Q-tip will start to change its color into black as the removal of some metal by the acid occurs.
Depending on your aims, the options include:
After obtaining the desired results it's time to make use of the acetone and cotton swabs for the removal of the etch resist. This will remove any sharpie marker or nail polish applied to the blade, pivot and lock face areas. After, reassemble the knife.
If there is no need to keep the acid, it is recommended to take it to a hazardous waste disposal facility. To neutralize the acid, you can make use of baking soda. It is still recommended to take the acid to a hazardous waste disposal facility after the neutralization because the solution contains a concentration of metals that could prove harmful to the environment.
There are a few last things that must be kept in mind which are:
The etching of aluminum with copper sulfate is less toxic, a safer, simple and cheap kind of electro-chemical metal etching. Aluminum etching is less toxic and is also a lot of fun to mess around with.
An example of a step by step aluminum etching has:
After the salt and copper sulfate has dissolved and the solution has cooled down a bit, the solution is ready to etch. In large quantities, copper sulfate is toxic; therefore you must protect your hands with gloves and also wear a mask and protect your eyes. If the solution has not cooled down yet, the etch is more aggressive and might even produce a smoke during etching, so allow it to cool down before using it.
A weaker or stronger solution can be made, or you can use the proportions of copper sulfate together with salt. It is also possible to do the etching process without salt, but then this will reduce the reactivity of the etchant. This solution can also be used in the etching process of zinc and steel, but not copper.
The etching process is really fast. With the proportions mentioned in the recipe above, it takes about 4 minutes to etch a line and obtain a light gray tone in 10 seconds and it takes 4 minutes to get a deep black. Unlike with copper and zinc, the lines are not that crisp, and since the time of the etching process is much shorter and the etch is more erratic, it is hard to play with different line thicknesses.
The mordant exhausts fast compared to other types of acids, though it is possible to recycle it. While in the mordant, it takes a very short time to cover the plate with copper sediments – the regular removal of the sediment with a soft brush or feather helps the etching process. It is recommended to use fine grain salt and fine grain copper sulfate because they dissolve better, even though if coarse salt is used, interesting textures in the aquatint can be obtained.
To etch lines, you can use charbonnel ultra flex. Always make sure that you draw your lines firmly, scratching the metal slightly. The lines are not consistent most of the time, as they are with copper and zinc.
Aluminum feels quite greasy compared to other metals due to its softness. This makes the ink really stick to it and it takes a long time to clean it, so you can add around 10% of softener to the ink. This will make it faster and easier to clean the plate and also makes the aquatint texture more even and finer. A softener makes a big difference in the printing process and result.
For the assurance of a long lasting bond between orthodontic brackets or composite material used for repair, ceramic materials and tooth structures, treatment of ceramic bonding surface is required. Various methods can be used for the stated purpose. They could be grouped into three categories, according to the mechanism of action. Methods of chemical, mechanical or chemo-mechanical surface treatments.
Surface acid etching can be used to achieve mechanical alteration. The chemical treatment is performed by means of universal or ceramic primers. The surface conditioning method selected depends on the ceramic restoration’s chemical composition.
Ceramics with silicon dioxide belong to the group in which the recommended surface treatment is acid etching. These ceramics include conventional or glass-ceramics. These include leucite-reinforced, feldspar-based, zirconia-reinforced lithium silicate ceramics, lithium disilicate, and fluorapatite ceramics.
The acids that are utilized as ceramic etchants are acidulated phosphate fluoride (APF), hydrofluoric acid (HF), and ammonium hydrogen fluoride. The most frequently used acid is the hydrofluoric acid, which when applied onto the ceramic surface, reacts with the silica matrix creating molecules of silicon tetrafluoride and water molecules that are released. The silicon tetrafluoride reacts with other hydrofluoric acid molecules forming a complex ion that is soluble, hexafluorosilicate.
Further on, the hydrogen ions react with the complex ion of hexafluorosilicate to form a fluorosilicic acid that can be rinsed off by the dissolving and removal of the surface layer of the glassy matrix that contains silica, silicates and leucite crystals, the surfaces becomes porous with a pore size of 3 to 4 micrometers. The acidulated phosphate fluoride has a composition of 1.23% fluoride ions that originate from sodium fluoride and hydrofluoric acid, acidified with phosphoric acid of 0.1 M concentration.
The ammonium hydrogen difluoride, NH4HF2 creates silicon tetrafluoride and ammonium fluoride when it reacts with a silica matrix. This acid is suitable for use as a glass etchant or as an intermediate in the production process of hydrofluoric acid. Different products may be used for ceramic etching. It must be noted that, besides their efficiency, these products are not allowed in some countries due to their highly toxic potential.
IPS ceramic etching gel, Ivoclar Vivadent, is an aqueous solution of 4% hydrofluoric acid in the form of a gel. This is unlike VITA ceramics etch, which is a solution that is alcoholic with a composition of 5% hydrofluoric acid and 10 % sulphuric acid. Porcelain Etch Ultradent has a composition of 9% hydrofluoric acid gel; primarily due to its high viscosity. According to the manufacturer’s instructions, it may be utilized in intraoral repairs of porcelain that has been fractured, in porcelain-fused-to-metal or all-ceramic restorations, as well as for the surface treatment of porcelain before placing orthodontic brackets.
Porcelain etchant, bisco, can be supplied in two concentrations that are different like 4% and 9.5% of hydrofluoric acid gel. There are two different types of porcelain etchants offered by mirage: 9.6% gel of hydrofluoric acid and 4% gel of acidulated phosphate fluoride. APF-gel may be made use of intra-orally and its indication is for luting of orthodontic brackets to crowns of porcelain.
The acid etching effect is dependent on the type of the acid and its concentration, the etching time and the type of ceramic being treated. Hydrofluoric acid is the most effective acid; increasing the concentration and the time taken for etching which increases the etching effect.
The type of ceramic being treated also determines the roughness of the surface and etching pattern; acids do not affect polycrystalline ceramics that consist of glassy matrices. Contrary, the matrix of silica and leucite crystals are dissolved selectively in glass-ceramics, creating a porous structure that is three dimensional. The effect cleanses the surface that bonds removing the oxides that are not wanted, and debris and grease. It increases the roughness, hence increasing the bonding area and wettability of the surface of the ceramic, and creates micro retention that can be infiltrated easily with uncured flowable composite cement, altogether increasing the resin significantly.
Acid type: The acid type determines the expressiveness of the surface micromorphology after acid etching. Hydrofluoric acid etching results in ceramic roughness that is higher compared to other acids that may be used for this purpose.
Acid concentration: the effect of acid etching does not only depend on the acid type but also on the acid concentration. An increase in the concentration of hydrofluoric acid increases the microroughness of the ceramic surface. A uniform crystal structure is observed as a result of dissolving the glassy phase when the performance of the treatment is done by hydrofluoric acid with a higher concentration (52%). Whereas a structure that is amorphous and also expressing large porosity can be detected when etching is done with a lower concentration (20%), when there is more dissolved crystalline phase.
Etching time is the time taken for etching by hydrofluoric acid affects the expressiveness of micro-morphological changes and microroughness of the surface of the ceramic. If the etching time is extended, the depth of the pores is increased.
To achieve excellent accuracy, photochemical etching can be used. Minimum standard etching tolerances are plus or minus 10% of the thickness of the metal that is being etched, to a minimum of plus or minus 0.025 mm. Greater accuracy can be achieved with development.
This chapter will discuss the applications and benefits of acid etching.
Acid etching can be applied in the areas listed below:
Acid etch tooling is digital, meaning to say component designs can be quickly set-up and optimized without financial penalty. There is no application of heat or mechanical force during etching, meaning the properties of materials are not altered and components are produced burr and stress-free. Nearly limitless part complexity is achievable, with an accuracy of plus or minus 0.025 mm.
Chemical etching is capable of producing very accurate engraved features right at the same time during the profiling of the material like fluidic channels, part numbers, or logos. These features come without any additional cost.
The benefits include:
Acid etching is the process of cutting a hard surface like metal by means of a specially formulated acid for the process of etching in order to allow for the creation of a design onto the metal. It is also known as chemical etching or photo etching. Acid etching can be applied on ceramic components as well as in dentistry. There are different types of acid etching techniques including total etching, selective etching, and self-etching. The effects of acid etching are affected by several parameters such as the acid type, the acid concentration, and the etching time. Therefore when performing acid etching, one must consider the type of acid going to be used, the concentration as well as the time it is going to take to finish the process of etching. It must be noted that even though the acid can also be neutralized with baking soda after etching, if there is no need to keep the acid, it is recommended to take it to a hazardous waste disposal
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