Page updated on April 1st 2011
As a small business owner, I have been designing & manufacturing telescope parts for over 15 years as the owner of a small but global company in that field "MoonLite Telescope Accessories". During this time, I have taught thousands of folks how to anodize their own parts with a small "home brew" setup. Anodizing is really not as hard as some anodizing shops would want you to think it is. Anodizing can be done in a very basic (home brew) way with a little understanding of the process. I hope you enjoy this page.
Business or hobby, if you work with aluminum, knowing how to anodize is a great skill to have.
BTW- I do not offer anodizing service, I would rather teach folks to do it themselves. It is very rewarding producing a great anodized finish on your own parts ! Please don't ask me to anodize your parts-- thanks -- I get many phone calls requesting the service.
The following procedure is for anodizing aluminum parts. Anodizing will protect the aluminum parts by making the surface much harder than natural aluminum. Aluminum oxide is grown out of the surface during anodizing and then becomes aluminum hydrate that is extremely hard. The porous nature of the anodized layer allows the product to be dyed any color that is required. The method I describe is Type II anodizing (room temperature) and gives an anodized layer of .0002"to .001" (half of which is grown into the surface and half out of the surface). Parts anodized will become slightly larger by about .0005" Type III (hard coat) anodizing is done at much colder temperatures and at higher current densities and can reach thicknesses of .002". Type III anodized surfaces can typically only be dyed black or dark green due to the denser pore size. I do not cover the hard coat procedure because it is not in the "home brew" category due to the colder acid temperature and high current density that would be required to perform it. The anodizing guide will show you how to perform the more popular Type II anodizing (Room Temp) using the home brew hanging wire method with materials found at typical hardware and auto parts stores (bare bones method). Almost everything you need can be found locally except anodizing dyes and sealer which I sell small quantities of on this site.
Here are a few parts on my brother-in-laws project car that were done with this system. The red pulley and water pump housing were anodized red (anodizing is not just for hose fittings). The photo below shows an after market skid plate that was anodized and dyed green to match the bike's colors.
Yes, just about anything aluminum can be anodized, even these aluminum horse shoes! However Cast aluminum does not tend to look good due to the impurities in it. For the most part, billet aluminum alloys anodized best.
A little custom color on your bike parts gives it a one-of-a-kind look. It is possible to do 2 tone color anodizing as these front fork tubes show - blue on the inside and gold on the outside. The anodizing guide discusses multi color anodizing methods.
Here is a sprocket that was striped of its original black anodizing and reanodized gold for a local drag bike. We also did the triple clamp in blue.
Notice the red battery tie down clamp, we anodized it red then engraved a logo into the red anodizing with our CNC machine
We andodized some custom gun parts in blue with a nice matte finish
This home brew process is type II class 1 anodizing and meets mil spec MIL-A-8625F as amended 15 Sept 2003 as it pertains to Para 18.104.22.168
Please e-mail any suggestions or questions concerning this procedure to Ron Newman.
We ship the latest Edition of the Anodizing Guide. "A Practical Guide to Anodizing Aluminum at Home"
The guide has more detailed information on anodizing that is not covered on this web page. The guide covers large and small current density anodizing methods from simple 2 gallon lines to larger chiller based cooled anodizing tank systems. This is a must for anyone wanting to setup an anodizing line with all the latest tips and tricks used today to produce spectacular results. If you would like a copy you can order online below (Pay Pal), or send a check for $28 plus $6 priority mail shipping (USA only) along with your return mailing address to----
Ron Newman 755 Preserve Danville PA 17821
I also take credit card orders over the phone.
Call 570-437-2232 10:00am to 4:00pm EST to place an order by phone, or use the online order form below (Pay Pal based) if you can. Also join the anodizing101 group on Yahoo. http://groups.yahoo.com/group/anodizing101/
New----Basic 2 Gallon Starter Kit
$154.00 for a 2 gallon anodizing line with 8 colors plus sealer and cleaner. Good for most common aluminum alloys such as 6061. Note: the Anodizing Guide is sold separately.
New----Advanced 2 Gallon Starter Kit
The 2 gallon advanced kit contains everything included in the basic kit above plus 2 gallon deox/desmut for anodizing alloys such as 2024. This kit works on 1000 to 7000 series alloys. Same exact anodizing chemicals used in modern manufacturing today,just on a smaller scale. The advanced kit also includes Aluminum wire and cathode plus Etch. Only $196.00 Note: the Anodizing Guide is sold separately.
Both the basic and advanced 2 gallon starter kits include the following 8 colors as shown (except Turquoise, Brown, Deep Red L, Olive Drab, Orange 3A).
Additional colors can be ordered individually if needed.
The guide and one of the 2 starter kits is recommended for first timers! This web page is only a sample of a home brew anodizing setup. You will still need to get a copy of the guide before attempting anodizing.
Besides kits, I also offer all anodizing chemicals in 2 gallon and 5 gallon quantities to make your own kit.- see order section below.
All dyes are professional anodizing dyes from "US Speciality Color Corp" same as commercial/industry uses. Plus new technology mid temp (180 degree) sealer. Black dye is the new BK Excel brand that gives a great jet black finish. These are some of the best chemicals out there today!
The basic and advanced kit will save most "do it yourselfers" money by not selling buckets, wire, fish tank heaters like other kits. I sell just the guide, dyes and chemicals that you can't get locally. Everything else like battery charger, battery acid, buckets, aluminum wire, heaters, etc, you can pick up cheap yourself. No need to spend a fortune on a high priced kit that includes items you may already have on hand.
If you do not have a suitable battery charger or power supply, we sell them separately below. We offer 2 different sizes of ASTRON Power Supplies a VS-35, and VS-70 version. They are adjustable from 0-15 volts DC and feature an adjustable current mode as well. They have both volt and current meters making them ideal for anodizing. The VS-35 model is good for small lines less then 10 gallons. The large VS-70 is good for 10 gallon and larger lines, plus it they can be stacked to provide expandability in a master/slave configuration. I use 3 of the VS-70s for a total of 210 amp capacity on my large 50 gallon anodizing line. You can pick the correct size power supply by figuring 12 amps for every square foot of part surface area to be anodized. A larger capacity power supply can do smaller parts, but a small power supply can't be expected to do large parts. Pick a power supply with a current capacity that exceeds the max current draw you expect to have. Remember, a current density of 12ASF is standard for type II anodizing as shown here. We also sell a 2000 Watt Heater designed to fit in a 5 gallon bucket or cooler. We now stock Titanium coils for a heat exchanger in the acid tank $200.
On-Line Order section using Pay Pal Please note: The Advanced kit and Deox/Desmut cannot be shipped outside the USA.
Guide and Anodizing Kits
2 Gallon Individual Supplies
5 Gallon Individual Supplies
Astron Power Supplies, Heaters, and Cathode/ wire kits
All Kits ship using UPS Ground.
There are basic steps in the anodizing process as illustrated above. They are covered in the anodizing guide and briefly covered on this page to give you an idea as to what is required. Not all steps are needed - such as etch and desmut - depending on what alloy and the type of surface you expect after anodizing.
To start, lets take a look at a fairly advanced anodizing line. The following photos show a medium anodizing station setup: A plastic tank for sulfuric acid in a sealed vented wood box, power supply, and optional AC unit. Normally an AC unit is not required, but this system was used continually and needed cooled down in the hot summer weather. A modest home brew setup could simply have a 2 gallon bucket as the anodizing tank along with other buckets/containers for dye and sealer tanks. A frozen plastic water bottle could be placed in the acid bath to cool it down if warm weather is a problem.
A cleaner, desmut, and sealer tank along with a sink.
This happens to be a larger 5 gallon line based on simple coolers.
Below you see a tank for each color dye. A 2 gallon container based line would be much smaller and less expensive. Small containers could be lined up to make a compact anodizing line. Of course you would be limited to doing only small parts. This 5 gallon anodizing line can do parts up to 17 inches long.
Here is my larger 35 gallon production anodizing line. It is a hand operated 7-color line that uses titanium racks. I also have 5 large Vibratory tumblers next to the anodizing line for mass finishing of raw CNC machined parts. I use 3 Astron VS-70 amp power supplies stacked for a total of 210 amps. The line has a 12,000 BTU chiller unit to keep the acid tank at room temperature when doing large numbers of parts at one time. The various titanium spring racks do not anodize along with the parts like aluminum racks do. Titanium provides electrical conductivity without having to be stripped each time like aluminum racks or aluminum wire require. The only maintenance for the titanum racks is to remove a little Oxide buildup once a year. Anodizing lines of this size and style can cost in the range of $10,000 and up for a small turnkey system. This system is not what I will talk about on this page as it is not in keeping with the "Home Brew" spirit. However, I wanted to show what a larger, more professional hand operated line could look like. This line allows more efficient anodizing of my telescope focuser parts for my business (MoonLite Telescope Accessories) and some occasional parts for the medical/surgical industry and U.S. government. I also produce some Ford Mustang performance parts as a hobby. If something is made out of aluminum--it can be anodized!
On larger systems like this, a chiller unit is normally required to keep the acid at room temp. Used chiller units can be found on Ebay fairly cheap. We sell titanium coils to connect to the chiller unit if needed. A closed loop chiller set up simply pumps cold water/ alcohol mix through hoses and Ti-Coil and back to the Chiller units reserve. The Titanium coil is the only thing touching the acid tank and will last many years. Larger coils of plastic tubbing can also be used as an heat exchanger in the acid, but is not very efficient. A Ti- coil is the popular heat exchanger material.
I sell the anodizing guide and small kits to small CNC style production shops wanting to anodize inhouse instead of sending their parts out, hobbyists, etc. A small anodizing setup will avoid the costly high minimum fees and long turnaround time of todays fewer and fewer anodizing shops. Most users report better anodized part quality than what they get from some of the pro shops!
Before we get to the anodizing procedure, let's talk about prepping the aluminum part.
First, anodizing hides no sins, so put a good finish on your parts before anodizing them. A good general rule is....what you see is what you get after the part is anodized; however, anodizing does tend to slightly magnify the surface texture so lean toward a smoother finish when prepping the part. Know that a small amount of the gloss will be lost after it is anodized. For a bright glossy surface on your anodized part, steel wool or wet sand it and then polish it with a buffing wheel using tripoli compound.
For a matte finish, just steel wool or sand it using an emery cloth.
There are other non manual ways to prep the parts surface before anodizing. I use vibratory tumblers with different grades of media for sanding and polishing the parts before anodizing them. This allows a large quantity of parts to be done easily. But for quick "one off" parts, buffing on a polishing wheel using tripoli compound is the quickest way. Or, you can just anodize the part right after machining it. Just make sure you clean the part first. Here is a photo of parts that came right off my CNC lathe. They were cleaned with simple dish detergent and anodized. No other prep work was done.
Multiple vibratory tumblers can also do finish work. Each tumbler can be dedicated to a different type of media. In this case, the first tumbler has 40 lbs of 1/4" plastic triangle media impregnated with silicon carbide to sand the parts. This tumbler runs wet and requires a flow-through water system to flush the debris out of the media. It runs anywhere from 3-24 hours, depending on the surface required. It will remove mill/machine marks and deburs all edges. The second and third tumblers use dry polishing media. Rougue treated walnut shell produces a bright mirror-like surface after about 72 hours. Each tumbler sequence takes between 2-24 hours to prep the surface. It is a slow process but many parts can be done without supervision or sweat. The tumblers and the media used in them are not cheap, so unless you need to do hundreds of parts at a time, I would suggest buffing them by hand.
-----Stripping or restoring existing anodized parts-----
You can strip off the existing anodized layer from any anodized part by placing the part in a caustic solution for an hour or so. Just mix a few tablespoons of lye and water in a plastic container. Wear eye protection and rubber gloves for this procedure!! Place the part in the solution and monitor its progress.
The Lye will dissolve the old anodized layer, about .001" thick. It takes a while for it to start breaking through the layer. It's a little slow at first. The first ten minutes or so not much action will be seen. Bubbles and smut will rise up as an indicator of its progress.
It is a good idea to help the process along by wiping the smut off the part to allow the acid to get to fresh aluminum. Just wipe off the part with a rag every 5-10 minutes until the old layer is completely gone (wear gloves and goggles). Only bare aluminum should be seen when the part is finished. If the aluminum part turns a dark color then it needs to be desmutted due to its alloy type. For example, 2024 aluminum alloy has 5% copper in it. The lye eats the aluminum off the surface but leaves the copper behind which in turn tarnishes to a dark color. Desmut is the opposite of a caustic solution such as lye. Desmut (normally ferric acid based) eats the non aluminum metals off the surface presenting a purer aluminum surface to be anodized. I include desmut in the advanced anodizing kit for folks doing unknown or non typical 6000 series alloys. It could come in handy and does not hurt to use it on all aluminum alloys.
Ok, back to stripping our part--
When the part is completely uniform (no remaining spots), rinse it off and buff it back to a shine. Stripping aluminum this way will create a matte finish. polishing it back to it's original surface is up to you. At this point, the part can be re-anodized and dyed any color just like a freshly machined part. Note: if the aluminum part has other metal or steel parts pressed into it, do not re-anodize the part. Metals other than aluminum will dissolve away during the anodizing process.
Here is the re-anodized part! See the anodizing guide for additional information on how to strip and restore aluminum parts
Restored browning gun parts.
Here is a part that all machine marks are removed and a nice matte finish was produced just by letting them in stripper for about 1/2 hour (etched). It really covered up any imperfections nicely. As you can see the part was then engraved with letters by machining through the dyed anodized surface exposing raw aluminum.
The finished part!
Enough about prepping and stripping parts. Let's get to the anodizing procedure.
The aluminum parts need to be clean. Oil from machining, polishing compound and fingerprints from handling the parts must be cleaned off.
The cheapest way of cleaning the part is to use dish detergent with hot tap water and scrub the part. Use a tooth brush to get into any tight corners if needed, or you can use a professional cleaner. Commercial anodizers always use a cleaner bath step. Here I am using the professional "740" aluminum prep cleaner that I include with the anodizing kit. The cleaner step requires the parts to soak for 5-10 minutes at 140 deg F. I use thermostatic controlled 1100 watt submersible heating elements in my tanks. A cheaper alternative is to use fish tank heaters or simply microwave a plastic container of the solution up to the desired temperature. The cleaner solution can be reused many hundreds of times. Note: most of my tanks use simple "aquarium" air pumps for agitation and have aluminum hanging racks to hang the parts from. You may also notice I'm using the same size 5 gallon coolers for all of my tanks in this example. This would be considered a 5-gallon anodizing line.
The hanging wire method requires----you guessed it, an aluminum wire connected to each part.
You can buy aluminum 12 gauge wire from McMaster Carr, MSC Direct, and other supply houses.
Connect an aluminum hanging wire to the part. This will provide the electrical connection when anodizing. The wire also provides a way of suspending the part in the various tanks (cleaner, dye, etc.) and keeps the part from being touched or handled. I force thread the wire into an existing tapped hole. Just double the wire up, or pound it to a point to fit your tapped hole. This connection must be very tight or it will fail during the anodizing process. Use pliers if needed to crank the wire into the hole. The wire is softer than the aluminum alloy and will simply take the shape of the hole without damaging the threads in your part. Remember, wherever the wire touches the part it will not anodize and will not take any dye. Pick the connection spot so it will not show on the finished part. If the part does not have a tapped hole then you need to get creative by pinching the wire against the aluminum or wrapping it around or through a hole. Just remember, where the wire touches it will not anodize or take any dye.
Setting up an ANODIZING tank---
Mix up a solution of sulfuric acid in a plastic container. The mixture should be between 15%-20% sulfuric acid to water ratio for standard type II anodizing. If you are using battery acid, it is already 35% sulfuric acid and 65% water by Volume, so if you mix 50% battery acid to water (equal amounts); that should put the ratio a little under 20% by weight. If you mix slightly more water than acid, it would be closer to the industry standard of 15% for type II anodizing. You can source sulfuric battery acid at your local NAPA auto parts store. Wear eye protection and rubber gloves when working with sulfuric acid. Remember the 3As rule!!!!! ALWAYS ADD ACID!!!! Never add water to acid. Please put a good amount of water in your tank first, then slowly add the acid to the water. If you add water to pure acid it could blow (boil) up due to the reaction. A good amount of heat will be noticed when adding the acid. By the way, the acid bath could last years if you are careful about rinsing your parts before putting them in it. Dragging chemicals over from previous steps is the quickest way to contaminate your acid solution. With a little care it could last a very long time, however, at some point (after approximately 100 runs) there will be too much dissolved aluminum content in the acid bath and will require changing the solution. A noticable drop in current density can be seen if the dissolved aluminum content is too high. If the acid bath turns brown or green then iron/steel or copper got in the acid bath and it should be replaced. Remember-only aluminum or titanium should be in contact with the acid. Stainless steel is OK around the tank but can't be part of the electrical circuit touching the acid. Stainless works well for fasteners, as regular alloy steel fasteners will rust quickly around sulfuric acid.
Note: Baking soda can be used to neutralize spilled sulfuric acid. Just sprinkle (more like dowse it) on until it stops fizzing.
Next you'll need a cathode or cathodes. Two cathodes, one on each side of the tank works well. The cathode is connected to the negative side of the power supply. Cathodes nowadays are 6061/6063 aluminum alloy. In the past, lead was used; however, lead sometimes has unknown alloy metals in it. If you want to be sure not to contaminate the acid tank just use 6061 or 6063 aluminum. The cathodes should stick out of the acid so a heavy gauge wire can be connected from the cathodes to the negative side of the power supply. The size of the cathodes should have at least 1/3 the area than the total part surface area. Remember, no other metal should touch the acid! If you have too little cathode area, then shadow effects (light /dark areas) can be a problem on your finished parts.
Just make sure you have enough cathode area and that they are spread out a bit.
The cathodes used in this tank are lead sheet.
6061 aluminum is used as cathodes in this configuration. It is recommended that the cathodes be removed when not in use over long periods of time, however, I don't bother. The aluminum ones here are turning black after about 4 months in the acid without being removed. A small amount of dissolved aluminum in the acid is required for the system to operate properly, so leaving your aluminum cathodes in the bath on a new batch of acid is a good idea. Anodizing a test part will also add dissovled aluminum to the bath helping a new tank break in quickly.
This configuration was one I used for small parts year's ago. It used small lead cathodes wired to the negative side of the battery charger using aluminum wire. Note the alligator clips for hanging the parts.
A battery charger or a DC power supply capable of providing at least a few amps of current is required. A small setup can use a manual 12 volt 6 amp battery charger, but I would recommend using a larger manual 12 volt 50 amp charger/starter if you have one available. DO NOT try to use an automatic battery charger. The automatic chargers get fooled by anodizing and ramp down the current, they simply do not work! The manual one used in this example puts out about 18 volts DC on the highest setting and will provide up to 50 amps. Next to the battery charger is a rectifier designed for plating and anodizing. It is a 15 volt 50 amp adjustable supply. It cost $500, the simple battery charger cost $80. The adjustable voltage rectifier can be adjusted to any voltage so as to produce the desired 12 ASF current density required. A typical battery charger only has a few settings and nothing in between so adjusting it is just a matter of picking the closest setting and adjusting acid strength and cathode area to dial in the correct current density. A new tank of acid will normally require about 12 volts to be at the desired 12 ASF current density, while a system that is broke in will require the normal 15 volts DC to produce 12 ASF of current density. Some folks will plug their battery charger into an electric light dimmer circuit to be able to control the output voltage and current. This works for small battery chargers, but don't expect the dimmer to hold up if a large 50 amp charger is used. A typical dimmer is only rated at 600 watts.
The larger the current draw, the faster the part will anodize. to much current can burn the part due to dissolution. High current anodizing also causes higher temperatures in the tank that can cause the parts to pit due to localized heat around the part in the acid. Again, use air bubble lines in the acid tank to keep things agitated and temperatures uniform. Don't try anodizing too fast at high current levels unless you have some experience with the process. Follow the current/time guideline below. This is what trips up first time anodizers, so please get the 2007 Anodizing Guide and test your setup on some scrap aluminum parts before doing real projects.
Anodize at a current density range of 12 amps per square foot of part area. Adjusting the acid ratio and cathode size will affect how much current is drawn during anodizing. Of course, the voltage produced by the battery charger has a great deal to do with current draw. Use different settings on the charger to try and stay between 12-15 volts DC and try for a current density of 12 amps per square foot of part surface for the normal 1 hour duration. Lowervoltage/current densities require longer durations and produce a more silver looking anodized surface. Anodizing at higher current densities is much faster and produces the typical yellow tint looking surface. Of course, the surface will be dyed anyway so the natural anodized alloy color is really not that important. however, the yellow tint will affect the dyed color a small amount.
My anodizing tank also has an electronic temperature gauge (simple indoor/outdoor gauge) to provide me a means of monitoring the temperature of the acid to make sure it does not exceed more than 75 degrees F while anodizing. The temperature of the acid rises while anodizing. The larger the tank of acid, the slower the temperature will rise during anodizing. Small tanks may only be able to do one run at a time before being forced to wait for the acid to cool back down. The part can start to burn or pit if the temperature of the acid is too high while anodizing. The ideal temperature range is between 68-73 degrees for Type II anodizing. My old system had an AC unit blowing into the sealed box to cool the acid down to around 65 degrees before starting an anodizing run. It could then maintain a normal temperature range with the AC running while anodizing. You don't need to have an AC unit like in this example if you are only doing a few parts. Most people would just do one run and then wait for the temperature to cool back down before starting the next. But too much of a "cold thing" is bad. Don't go below 65 degrees! The colder you make the bath, the less current will be drawn for a given size part. Anodizing at 50 degrees would require double the voltage coming out of the power supply. A typical battery charger is only going to put out between 15 to 20 volts so it will not work. Stick with the normal range of 68-73 degrees for Type II anodizing. 50 degree anodizing is basically hard coating or type III anodizing; however, the required current density is 24 ASF and at that high of current level much higher voltages are required.
By the way - a stick-on fish tank temperature gauge also works well for monitoring the acid temperature.
Next, suspend the aluminum part in the acid using the attached aluminum hanging wire. Connect the positive terminal of the charger to the wire holding the part and turn on the charger. The part should not touch the plastic container or be placed too close to the cathodes in the tank. See the Anodizing Guide for information on "how to" build aluminum racks and related rigging methods. Titanium wire can also be used and does not anodize along with the part. It can be used again and again with no stripping involved. Aluminum wire anodizes with the part and once anodized does not conduct electricity, therefore it needs to be stripped back down to raw aluminum before being reused. Normally, the wire is discarded after being used once.
Ramp up the voltage slowly if possible. Start the charger at the lowest setting for a few seconds then click up to higher settings until a good current density is being drawn. Sometimes applying full power abruptly can cause the electrical connections to fail at the wire to part contact point. If the electrical connection to the part is not tight, it will fail during the process and only the aluminum hookup wire will be anodized, not the part. The current should rise then level off in the first few minutes of anodizing. As the anodized layer finishes building on the part you may notice a small drop in current, about 1 hour into the procedure. However, if the current drops suddenly early during the process that indicates that the connection to the part has failed. If the current is too high, the connection wire may burn off. Use a 12 gauge wire when possible for the hanging wire. If the current keeps rising as the part anodizes then check the temperature. The hotter the acid gets the more current will be drawn. Remember, the temperature has to be kept within limits or your part may become pitted.
Bubbles will start foaming off both the cathodes and a little from the part. I would advise not breathing the fumes, and would suggest some way of venting them away from your work area. I put the plastic tank in a sealed wooden box with a fan to vent the fumes out a nearby window using a simple dryer hose.
Next lets figure duration, it is important to anodize for the correct amount of time. There is a point in time as the layer is grown that the process reaches the dissolution point. Where the coating gets no thicker (typically .001") and the sulfuric acid is eating away the layer at the same rate it is being grown. If the dissolution point is exceeded then the part will start to "burn" or look pitted. Decorative anodizing is about halfway to the dissolution point and is common on manufactured items that durability is not a factor, but color needs are.
Figure out how long to anodize the part using the following Duration rule - 720 amp minutes per square foot of part or 12 amp hours per square foot of part for close to full thickness (just under the dissolution point), Remember the current density is normally at 12 amps per square foot for exactly 1 hour. Duration and current density are two different things!! The Duration and current densities are covered in the guide.
The sample part in this example is not being anodized at the regular 12 ASF rate. It has 42.4 sq " of surface and is drawing 2 amps according to the meter on the power supply. 720/2 =360 amp min, and 42.4/144 = .294 sq'. So 360 times .294 = 105 minutes in the tank. The current will automatically adjust for more or less parts up to the capacity of the charger's amp rating being used. So, stay under its maximum rating or the charger may overheat. Your anodizing setup's current density and anodizing rate will differ due to different battery chargers, tank sizes, acid ratio, and cathode sizes. Anodize a 1 square foot test part (12x6" sheet) to see what current density your system wants to run at, adjust the setting on the charger, acid ratio, and cathode size to get the system to operate up to the standard 12 ASF density range. Then calculate the duration based on the current draw and do some scrap parts to see how everything is working. In a perfect world, 12 ASF for 1 hour will normally require 70 degree acid, normal cathode to part ratio, 15 volts DC, 6061 aluminum alloy, and some dissolved aluminum content in the acid (broke in system).
Notice the color of the anodized part. Most alloys show a pale lemon tint if using a higher voltage based current density range. The following photo shows the color of three 2024 aluminum alloy samples - natural aluminum, anodized, and dyed black.
Can you tell which part below lost it's electrical connection during anodizing by looking at the color?
The 2nd from top/left failed during anodizing. See the lighter shade, unlike the others.
Rinse the part with COLD water after removing it from the acid tank. Do not use hot water as it may start to seal the pores in the aluminum hydrate layer before you have a chance to dye it. Once the part is rinsed, it is time to dye the part to your desired color.
Violet dye was used on this Jr. dragster.
Mix the dye according to the manufactures instructions. Most of the powder based dyes mix at 2 grams per liter of water, (there are exceptions - one is black dyes which tend to be about 4 times that). Heat the dye to about 140 degrees F. Hang your anodized parts in the dye bath for anywhere from 15 seconds to 15 minutes depending on the shade desired. If you want a light pastel shade of the color, keep the time short. If a deep solid color is what you are after, let it in the dye for the full 15 minutes. Anodizing dye will last years if you are careful not to cross contaminate it with sulfuric acid from the anodizing step. Remember to rinse well between tanks. Also, don't forget to seal the dye container when not in use to prevent evaporation. By the way - just add a little water to the dye, anodizing, cleaner, and all other baths to bring the water level back up due to evaporation. I check and adjust mine before each use.
Here is a 5 gallon blue dye tank with the heater pulled out and hanging rack installed. You can simply use a plastic container and microwave it to heat up the dye if needed. (your wife will love you for this one) It does not have to be anything fancy.
Rinse the parts after removing them from the dye tank. Now it is time to seal the pores and lock in the dye by sealing the part. All commercial anodizing dye requires a Nickel Acetate based sealer. Just place the parts in 170-180 degree sealer for 20 minutes, rinse, and let dry overnight. Stay away from the low temperature sealers as they tend to leach out a good deal of color during the sealing process. The new mid-temp Nickel based sealer is what I offer in the dye and sealer kit.
If you do not want to dye the part and just want to seal the natural anodized color, just skip the dying step and seal it as outlined above. The natural anodized color will change slightly.
If the part does not take the dye, it means it is not anodized fully. Look for failed electrical connections, too little current draw, not long enough anodizing time, too small of cathode size, automatic battery charger or too weak of acid. Check the wire, if it takes the dye but the part does not, then the connection failed at some point during anodizing.
Note the middle part failed to take the black due due to not being fully anodized. The electrical connection was at fault. The part was returned to the anodizing tank BEFORE sealing. It was then anodized fully after fixing the connection and re-dyed.
For anodizing other aluminum alloys such as sand cast and dye cast aluminum special prep is required. The Guide has limited information on anodizing cast aluminum. It is notorious for being the most difficult aluminum alloy to anodize due to the high silicon level in the alloy.
Plastic coolers, buckets, and storage containers all work well for setting up an anodizing line.
Please see the booklet for splash, fade, mask and other multi color dying procedures along with masking steel parts to protect them prior to anodizing.
Doing fade and multi color anodizing is great fun if you take the time and practice. There are amateur anodizers with very small modest systems doing outstanding multicolor parts.
This was a simple 2 color fade job. The Guide will show you how to do multiple color fades, splash, and other cool effects.
Here is a 2 color splash anodizing job using hot pink with orange splash. If you are the creative type you can see the possibilities doing multi color anodizing. It is not hard, it just takes a few practice scrap parts to get up and running.
Top of pageRevision 04/01/11