I noticed something similar to this recently. It only shows up on the application of the second coat of sensitizer. When you go to put the brush down for the first time, you need to make sure that you place it into the middle of the puddle of solution, not on a dry portion of the paper next to the solution.
The water in the brush will start to dissolve the first coat a little if you don't get it into the solution, and that can result in an unevenness in the final print. If you start by dipping the brush in the solution, then the water is not an issue, and everyting will go smoothly.
When I do test strips, I use a large piece of paper similar to the size of the print, and then cut strips out of the paper. this eliminates some of the variability associated with changing the coating size, etc. This is one case where I disagree with Dick's book, because I don't think a small test strip coating is ever going to be equivalent to a large sheet coating. They are not scaleable in a predictable way.
This is a good reason for people to sort their paper when then get it. If you have paper with defects, these are the logical pieces to use for the test strips. When I cut a large piece down for a 7x17 print, I am often left with a scrap of paper and two banquet sized pieces. I sort as I cut down, and if one of them has a defect, then it goes into the test sheet pile. The scraps are actually large enough to use for tests also, so I manage to have little waste.
re: metal ferruled brushes with platinum. It's a common question. For some reason, that dictum has gotten passed around in the platinum printing world since god was a kid. Like sightings of Elvis and JFK riding around together in a convertible in the Nevada desert, it sounds plausible, but doesn't prove to a problem in actual practice. I have been using the same Richeson brush for two years, and the only noticeable effect was that my prints got better. But the question always seems to come up. Anybody have an idea what book first mentioned that warning?
I've been using the 9010 brushes for some time now with no problem. The metal ferrel discolors a bit but no problem. The biggest problem is the paint cracking and falling off with the 2 inch model. The 1 inch model doesn't have this problem.
These ferrels must be a good grade of stainless steel.
Chalk that one up to "Urban Legend" status. I have never seen a negative result that would even be construed as a result of metal in the brush. Yes, if you have a sloppy, rusted brush that is dropping junk everywhere, then you could have an issue, but if you keep the brush clean and in good shape you won't have any problems.
Sometimes people get spots on their prints, and have difficult determining where they come from. I think someone along the line thought that it may somehow be a result of a flake of metal contaminating the solution. Then, looking around the lab, decided that the brush is the most likely culprit.
Rather than the brush, I think it is far more likely that contamination is a result of the heater element in a hair dryer beginning to expel some pieces of metal as it ages.
The most likely source of black spots is the metal salts. Platinum is close to saturation, so some can drop out of that if it gets too cold or some of the H2O evaportes off. Palladium can also get some 'grit' in it. It looks like carbon, but it isn't from a supersaturated condition.
The best thing to do is be very aware of the condition of your metal salts, and filter them through filter paper if they show signs of the 'grit'. If the platinum has crystals in it, you can add a few drops of distilled water and then heat up the solution, and you should be back in business.
yeah some times as photographers we tend to make things more difficult than they are. If you stop to thnk for a moment, in the 18 and early 1900's they did not use special brushes, or have destilled water for their solutions and I am sure the refining techniques for pt and pd were not up to todays standards, yet they managed to make wonderful prints.
I am sure using destilled water is a good practice, but I have been using tap water since I moved to mexico to mix ALL the solutions, and have not noticed one bit of a difference from when I used destilled water.
The biggest problem is the paint cracking and falling off with the 2 inch model. The 1 inch model doesn't have this problem.
Go the hardware store and buy some tool grip rubber handle goo. It's the stuff you can use to make your screwdriver handles grippable. Just paint that stuff on your brush handle and hang it bristles up to dry, and it makes a nice non-flaking coating that is cool and sort of hip-industrial.
And maybe metal ferrules are something that you need to avoid with Van dyke. I don't have enough experience with Van Dyke to say one way or the other, although when I have done VDB prints, I use a non-metal Hake brush, because that is what I had available. I do think it is advisable not to mix processes with the same brush. I have dedicated brushes for platinum/palladium, VDB, cyanotype and teeth.
If you go to coat the brush with the plastic handle stuff, first take very rough sandpaper and score up the finish a little so it will stick effectively. The first time I did this, the brush was brand new, and it started to peel off pretty quickly.
I stripped the handles of my brushes, and then used a spar varnish on them. That has worked out well so far, with no cracking of the varnish to report.
I'll check on that brush coating goo at Lowes or Home Depot. Wonder if it comes in wild colors?