Originally Posted by bridog
haven't done a chemical etch in many years (that was zinc plate using nitric acid). I remember this was pretty nasty stuff and required us to wear heavy duty gloves, facemasks and have pretty strong vacuum type venting in the print lab. Just reading up about aluminum plate etching. Has anyone done any etching using this metal with chemical baths such as stannous chloride or ferric chloride? If so do you require ventilation like you would etching using nitric acid?
I understand these are safer alternatives but can't seem to get much info about the actual safety aspects of working with these particular chemicals.
Think I read you need to etch aluminum plate in ferric chloride by inverting the plate to face downward in the bath.
I am also curious about the alternatives to coat your plate with instead of asphaltum.
Lots to learn and I would like to know other's experiences with the newer materials and mordants.
I etch aluminum plate all the time. Stannous chloride and ferric chloride are both pretty nasty, and I would not use them. There is a very old technique (hundreds of years old) that is good for aluminum, zinc, and steel ... but does not work for copper. And it is about as low in toxicity as anything you will ever use.
You will need the following chemicals:
copper sulfate ... sometimes called blue stone ... used as an anti-fungal spray for fruit trees and as a foot bath for sheep and cattle to combat foot rot ... try a good garden store or a good farm supply store ... comes as coarse blue crystals
sodium bisulfate ... used to adjust the ph of swimming pools and hot tubs ... one brand is called PH Down ... buy it in pool supply stores or Walmart ... comes as a white powder.
table salt ... get the non-iodized variety from your local grocery
Mix these three together dry in a plastic container. Use a scoop, like a table spoon or coffee scoop to measure as follows:
copper sulfate ... .. 9 scoops
sodium bisulfate ... 2 scoops
table salt ............. 9 scoops
In other words, the proportions are 45% copper sulfate, 45% table salt, and 10% sodium bisulfate.
Make a concentrated solution of the mixed powders ... fill a glass or plastic jar with water and then add several scoops of the powder. Put a lid on the jar and shake the bejabbers out of it to dissolve all the powder. Repeat the process until you cannot dissolve any more of the powder. Your solution will be a lovely blue.
For a resist, I use shellac from the hardware store because it is cheap, pretty non-toxic, and it dries very quickly. I color it by cutting open a permanent red felt pen and putting the ink soaked felt directly into the shellac. That way you can see any gaps when you coat your plate. I have also used oil-base inks for a resist ... but they must have cobalt drier added or they take forever to dry. If the shellac needs to be thinned, use Denatured Alcohol from the hardware or paint store ... that is just ethanol that has a small amount of something noxious added to keep people from drinking it. Ethanol is grain alcohol .... booze ... and will not harm you if you get it on your skin. You could use 99% isopropyl alcohol from the drug store, but that is expensive. Avoid methanol, as it is carcinogenic.
For plates, I often get used aluminum off-set press plates from a local print shop for nothing. Or I buy rolls of aluminum flashing from a building supply store ... you can buy it in several widths by the foot. I use acetone based contact cement to glue the thin aluminum to plexiglass to give it some backing and make it easier to handle. Cut the aluminum with a guilotine paper cutter or score with an snap-off blade cutter and bend a few times to break it. Bevel the edges of the plexi-aluminum sandwich with a file and sandpaper or with an electric sander. Once the sandwich is made, use a palm sander to smooth the surface of the aluminum and remove any old ink or other material that may be on the surface. Start with 250 grit sandpaper, go to 400, then to 600, and even to 1200 if you want almost no plate tone. these high grit sandpapers should be available in automotive supply stores if your local hardware does not have them. Then just use a paint brush to coat the aluminum with your resist. You will not need to coat the back of the plate, as the plexiglass will not be affected by the mordant.
I have also used galvanized steel plate. You can find a shop that makes heating duct work in almost any city of any size. Or check with a machine shop. They should have a variety of steel plate available and can cut it to size for you. Or you can buy a larger sheet and cut it yourself with a power jig saw and metal cutting blade. Steel plate of 16 guage or so will not need any backing. Again, bevel the edges with a file. Then use a paint brush to coat both sides of the plate. Mild steel plate or galvanized steel plate will not need to have the surface sanded or polished, but you should clean it well to remove any oil or grease.
Needle your design through the resist as usual ... if you slightly warm the shellac you can get finer lines ... but be careful with your warming the aluminum/plexi plates or the plate will warp because the aluminum and the plexi expand at different rates.
To etch, just put the needled plate into the mordant bath. Aluminum will etch in 2 minutes or less; zinc plates take about 15 minutes; steel plates take about 30 minutes. You will see a brown sludge forming ... that is pure copper. The metal (aluminum, zinc, steel) goes into solution, and the copper from the copper sulfate precipitates out.
If etching steel, you will get a brownish scum on the surface of the solution. That is iron oxide and is very staining. You can pour the used mordant through a coffee filter to remove the scum. If etching aluminum, the solution will stay clear.
Wash your plate with water to check your etch. Return it to the bath for more etching if necessary. When done, you can use concentrated orange cleaner (from your hardware store or building supply store) to remove the shellac. You could use alcohol to remove the shellac, but it is very volatile and expensive. To remove an ink resist, I use acetone. Acetone is very volatile and highly flammable, so use it outside or with plenty of ventilation. Actone is not a neurotoxin (but just like alcohol, it will make you woozy if you inhale lots of it), it is not a mutagen, and it is not carcinogenic. It is produced naturally in the body and is eliminated from the body. So it does not accumulate in the body. It is MUCH safer than lacquer thinner, turpentine, and other solvents.
This mordant solution will not hurt your skin. It is not corrosive. It is not absorbed to any significant degree through your skin. It may stain your clothes if it gets on them, but it will not eat holes in your clothes. The only gas given off during the etch will be a small amount of hydrogen, which is of no concern. The solution is toxic if you drink it, so do not drink it and do not leave it where a kid might drink it. An adult would have to eat several ounces of copper sulfate to be fatal. Sodium bisulfate is about the same toxicity as table salt. If an adult were to eat a teacup or two of ordinary table salt it would be fatal. But we do not regard table salt as highly poisonous.
You can use the mordant over and over, but it will be depleted in time ... gets more of a greenish hue rather than the nice blue color. Store it in a well marked plastic container with a plastic lid. To dispose of it, just dilute it with water and pour it down the drain. Certainly in the amount you will be using, it poses no environmental danger ... no more than than spraying fruit trees or draining your hot tub or flushing your urine down the toilet.
Hope this helps.
Cheers ....... Charles