Now, as I said in the first post, these are notes from a few months back, so some are a little out of date. I only post them as a record of the process I went through to get to a solution. I have edited out some of worthless stuff and added notes to things I have since changed or discovered better solutions for. You may skip though as much as you see fit, or do like I do and just look at the pictures.Working on the computer has advantages, but because you can zoom in on the computer screen to such an extent, it is easy to loose a sense of actual size of the artwork. Elements you think are "big" turn out to be far too small. So the first test (on the right) resulted in the lines being too thin. The second test yielded a much better result.
I still have to draw the vine pattern down the center of the figure eights, as this amount of curve change using the envelope tool will distort the pattern to greatly. The result I fear, would look too "computerized". Also on this test, I added the dots with paint pen and they are too sloppy. Part of this was my not taking enough care when applying them, the other issue is the pen does not deposit enough paint in a small dot. It has been suggested that I use a tube style applicator which is likely the best tool for the job.
I received the 99% acid, so I'll make up a new batch of paste with a 50% "vinegar" and see how this affects the etch. I also opened my 20lbs bag of copper sulfate and the grains are much smaller than the sample material I had purchased from McMaster Carr. This should help in the material going into solution quicker. They also sell salt flour or popcorn salt, which is also finer grind. At some point I'll try this. I chose to buy "raw" copper sulfate and not to use "root killer" CS just in case there were other additives or some type of dilution.
I may increase the ratio of salt, in a separate test, since my first test (test 1) I had not had the recipe in front of me and I mixed the CS and salt 1 to 1 and the etch seemed a bit more aggressive.
Did some new tests. I have made a few different batches of paste with the 5% and 50% vinegar and there is not a noticeable difference. I have tried 60, 90 & 120 minutes etches, as well as a few in the 4-6 hours range. It seems multiple 60 minute sessions are better than fewer longer sessions. The issue is the copper build up on the etched surface, which needs to be cleaned off between applications of the paste. (Found a solution for this) If this copper deposit gets too thick, it seems to get under the vinyl masking easier and lift the mask off.
I have also tried a new, thinner vinyl and a special paint masking vinyl. As suspected, the paint masking vinyl does not have aggressive enough adhesive and weeding it on the steel is unsatisfactory. This masking vinyl is very expensive and luckily the shop gave me a sample to test.
The thinner vinyl is an inexpensive product from China and works well. It's adhesive seems very good, although I suspect a name brand material may be a bit better. (turns out, maybe not) This test was 4 applications at 60 minutes each. Perhaps 3 applications at 90 minutes may also work. The dots are, I think, as small as the vinyl will tolerate, without being pulled up while weeding the background. They are about 1 mm (.040") in diameter.
I also tried a simpler vine pattern on the sides, but I don't like it.
Robert MacPherson has done some research into these pastes and how they were used. He told me, one of the period descriptions he read, said that the paste was applied about the thickness of one's little finger. That seems to be what I'm getting.
I'm pretty happy with this recent test and it seems I'm back on track with a technique that works consistently. I have ordered some pen plating supplies with guidance from Mac. So when it arrives, I start plating tests. Then the bluing salt.
In the meantime, I'm finishing up the artwork for the front of the greave and will start etching the sabatons. I have been finishing the figure eight/ lighting bolt design and testing different mixtures of paste and different etch duration's.
1: Ratio- 1 parts salt / 2 parts Copper Sulfate / 1/2 part Vinegar. (I have a newer version of this)
Mix well and add more vinegar as needed when solids start to dissolve.
As the solids dissolve, the mixture changes color from aqua green to lime green and gets creamier. To aid in liquefying the solids, I ordered Copper Sulfate on Amazon that was a finer grind than the "root killer". I have been using regular table salt, but I think if you use popcorn salt or "salt flour", (finer grinds of salt) this may be beneficial. I did a side by side test with too pastes, one with table vinegar, 5% and the other with 50% Vinegar. There seemed to be little difference in the etch depth over the same amount of time. However, the 50% paste did more damage too the vinyl material, causing more tiny elements (dots) to come off. I also tried 1 part CS to 1 part salt, but this did not seem to increase the etch much, if at all. Temperature; My first tests were during some hotter days here in LA, so I though this may be affecting the etch depth. I tried heating the plate during the etching with a light bulb and just at the cooler room temp. (70 f). I observed no significant effect.
2: Fresh etching paste seems to be key. (Maybe not)
I'm not 100% sure on this (I'm testing fresh verses old material now), but recently I had a number of tests that were not as deep as my early tests. When I compared them, in date order, it seems the older the paste, the less aggressive it became. I was getting frustrated since it seemed, as I advanced in developing the artwork and masking techniques, I was going backwards in the effectiveness of the etching. It does seem like 4 to 5 day old paste is the culprit. If there are any chemists out there, I'd be curious to hear why this may be.
3: Etch times 1 hour to 3 hours each application.
In my first tests, I had been etching 60 to 90 minutes per application. Being careful not to destroy the resist during the cleaning. The etch process leaves a copper build up on the surface. This layer seems to either get under, or stick to the vinyl masking. If it gets too heavy, it pulls more vinyl off.
I have found 3 to 4 applications at 90 minutes each worked very well. However, last night, I left one test plate overnight for the 4th and last application of paste, and it came out perfect. So I'm testing two & three, 3 hour applications to see if I can leave it this long and still preserve the masking. I think the paste can be left on until it all turns brown / black. Over 90 minutes, only about have the material has blackened. The uppermost surface is still green. Mac mentioned a period source saying the paste was applied at a pinky fingers thickness. I believe this may be to facilitate longer etch times, since once the paste is black it seems no longer effective. The most recent test over night (about 7 hours) most of the paste was black and much of the masking lifted during surface cleaning.
EDIT-Current formula (as of July 2021) After over 100 tests and 99% of the armour complete, the formula I'm using now with satisfactory results is:
100g fine salt (Salt flour)
100g Copper sulfate fine crystals
25g Bone charcoal
13g activated wood charcoal
Distilled water to make it a thick paste.
The reaction with the salt, will cause the material to freeze, so after mixing, you need to let the paste sit for and hour or so, and then t\remix it. NOTE: Do not make your initial mixture too wet, as after you remix it, the salt gives up some water, and the paste gets wetter.
If it is too runny, you can add charcoal to thicken. I have found 3 or 4 90 minute etches (fresh paste for each) gives you considerable depth, equivalent to late 16th C armour.
Masking, Better vinyl works better and lasts longer. I have the cutter now effectively cutting background dots at less than a mm and adhering to the metal sufficiently to arrive at an acceptable etch depth. The new vinyl can be mostly weeded on the backing paper, which is much faster than pealing the excess material off the metal. It's only the areas with the dots that have to be removed from the steel now. Because if this is done on the backing paper very few of the dots stay.
I still have not picked up the name brand vinyl sample from my graphics guy, but this generic material seems to work pretty well. If you get the cutting knife depth dialed in along with the cutting pressure, the machine cuts the vinyl without lifting up too many dots.
Still do not have an effective paint type mask that lasts. Testors model paint, fingernail polish, enamel spray paint, paint pens, sharpies, work for perhaps one etch application, but come off fairly easily. The fingernail polish is the most effective of the materials I've tried. I have ordered some asphaltum to try.
I'm sure if I had the drawing skills, this would be a faster process with the proper masking medium and a pen or brush. But I'm forced to use the tools I have the skills with when faced with this much artwork.
Here is the latest test: 3 applications of fresh paste for 90 minutes each and a 4th application for 7 hours. (You will notice a misalignment on this vinyl mask cut)
The etch depth is the best I have gotten so far. It's about .008" deep. This is now looking like the etch depth of the real armour.
I had considered bees wax as a way to get specific dots. I'm not sure the best way to apply them. It may be as easy as a large straight pin.
For the test, I used fresh, 1 day old and 2 or 3 day old. They were nearly a factor better than each other, the newer the paste cutting at least 10 times the depth of the 3 day old paste.
Here is a close up of the real armour, it seems I'm getting close.
I also received the pen plating supplies and at first I thought my rectifier was not working, but it was just that it had been sitting so long (10 years probably) that the variable resistor coil was corroded and needed cleaning. So I plated a couple of the earlier test etchings.
I also got out the bluing salts.
It's hard to see in the photo, but the blue is electric when the light hits it just right. The gold also yellows considerably with the 600 degree heat. Again, it is hard to tell in the images, but I went over one band of gold with fresh plating to bring it back to a lighter, less orange gold.
Controlling the color on the big pieces will be difficult, but on this first try, one piece went through blue, to a grey color. The piece pictured above was a shorter duration and the salt had cooled down some. It turns out the salt wants to be at 550 f, not 650f as suggested. So if I find the sweet spot as far as temperature goes, the color may be easier to control.
Today was cutting masks and adapting them to the greave. I have to start with the main pattern on the front plate, so I can cut sections to fit the lames while matching the main pattern. I still need to add the wider vine boarder on the sides and mask the large area on the main plates.
I have done about 40 different tests, using a combination of ingredients and ingredient ratios, (Copper sulfate, Copper acetate) as well as different etch times and number of etchings. I have also practiced ways to repair the vinyl resist with asphaltum resist, since with multiple application of etching paste, the material can start to lift, or at a minimum, I loose dots. The best applicator for the I have found for the asphaltum resist is a "Henna" applicator bottle, available as a kit from Amazon.
The batches I have been mixing are: (by volume)
(I have since developed a better recipe)
3 parts fine salt (I bought a large 196oz. container from "Smart & Final" a local restaurant supply)
6 parts Copper Sulfate This is a much finer grind than the "weed killer" variety.
1 to 1.5 parts 7.5% Vinegar
The trick is to mix the salt and copper sulfate together, then add the vinegar and mix. It will seem like too little vinegar, but after mixing, let the mixture sit for 1 to 11/2 hours and re-mix. There is water trapped in the salt (and possibly the CS) and as the solids dissolve the extra water is released and the mixture changes from a "wet sand" consistency to a smooth paste. This is important if you want to make it stick to a vertical surface. Too much vinegar and the paste will get runny after it sits for awhile.
Here is the first section of the armour to get etched. It's the front of the left greave with the ankle lames. I had etched this piece earlier, but the copper buildup from the etching process was difficult to remove and I was concerned about damaging the vinyl resist so I let the paste sit longer and this did not work well. As a result, I had to very carefully sand down the etched areas and re-polish. Thankfully Mac and Jeff planish very well before sanding, thus the already thin metal was consistent in thickness and I didn't run into thin spots while sanding. (Something that cost me two greaves when I had made them for my 1330's kit. :x )
Here is a close up of the center of the greave. This was 4 applications of paste at 60 to 70 minutes each. You can see some of the "repaired" dots. I may abandon the dots in the vinyl and just add them with the asphaltum resist straight away.
I would like it a little deeper, but the vinyl is so fine, it begins to lift on the 3rd application. Longer times seem to be less effective. 60 to 90 minutes gives a good etch and still allows the copper deposit to be removed easily. On the larger pieces, where the pattern is larger, I can probably etch 5 or 6 times, to get it deeper. In the close up images I have of the original armour, it looks like the breast & back are etched deeper. I have fully etched to front of the left greave and have most of the back masked.
I have taken to putting the background dots on with the asphaltum resist, as this makes them more durable and makes cutting and weeding the vinyl easier. I am also reinforcing thin areas and loose ends of the vinyl masking because these are the areas that are the most vulnerable during cleaning between paste applications. This is the back plate of the greave and the different tools I'm using to apply the resist. Now that I have the system down, I should be able to get the right greave done in 2 or 3 days, (Yeah, Right!) unless I get interrupted. (Like I may have to go to South Africa next week)
Next: Viewing the Master's work....Well, I thought it looked good....