Would like to know if those who use platine are using an oxalic acid bath and double coating or just one or the other. Thinking maybe the first coating of the sensitizer would add enough acid so the second coat wouldn't know the difference. I know I could try it myself and find out but would be interested in what others are doing and results they are getting.
I don't precaot with oxalic when using Platine. I have found that Platine will make good single coat prints, but the paper really does look better when double coated.
However, doule coating has been difficult for me, as I have found that rod coating produces completely unacceptable tone 'grain' and I get a similar problem using Hake brushes. I even tried rod for the first coat, and Hake for the second.
That all changed when I started using the Richeson 9010. I'm now completely satisified with double coating for this paper, and also Cot320, which is very similar.
I did some tests pretreating with oxalic, and I didn't see an improvement in the paper with this step. In fact, due to the extra step swelling the paper fibers, I recall I was getting a slightly worse single coat after the oxalic acid pretreat.
Ultimately, you need to find your own method, because what may work for one, may not work for another due to environmental conditions or other differences. So you might want to try a few tests to see for yourself. Take a sheet and precoat half with oxalic, and then let it dry. Then coat as normally, and see what the differences are. They should be readily apparent in the print or test strips.
FWIW, there has been some speculation that in some cases, the oxalic isn't really the issue, it's the H2O that is being introduced. If the humidity is low in your workspace, precoating with distilled H2O is similar to creating a localized moist envoronment, which will definately affect the quality of the coat.
I switched to the 9010 brush several months ago and I'm still amazed in the difference it makes.
When I pretreat the paper with oxalic acid I do it several days in advance so it is dry when I use it. I have found that if I just let the paper rest for 5 minutes and use a cold air setting on the dryer after coating that I get much better blacks (of course I'm talking about the sensitizer here not the oxalic acid). The added moisture makes a big difference. First couple of times I was a bit nervous, thought maybe the added moisture would mess up a neg but no problem so far. Nothing has plated out on the negative.
Just mixed up a fresh batch of ferric oxalate and plan on doing a bit of testing this weekend.
I typically coat the paper, and let it air dry for 30-40 minutes. Then I coat again, and let it air dry for 5-6 minutes. Then, I use a hair dryer on low heat to dry it to the touch. As I said, I don't find that I need to use oxalic. The RH in my darkroom is almost always about 50% minimum, and will go higher in the summer. I use a timer so I am somewhat consistent about the coating procedure, and it seems to be quite consistent.
That has worked well, and the second coat definitely increases DMAX, and also improves shadow detail.
I have found that I get slightly higher contrast with COT320, but the dmax appears to be about the same. The differences between the papers is subtle. It also appears that the COT320 has fewer imperfections. I have mostly switched from Platine to COT320 because it seems to be a bit more consistent for me.
I have about the same RH in my darkroom. I've got both cot and platine on hand so I'll try both. I agree the cot usually has a lot less junk in it but not always.
Do you use a "full load" for each coat or dilute?
I have been using a full load, but I suspect that the first load could be diluted with some H2O or alcohol to cut costs. I have not done tests on this yet, because frankly, I'm about sick of tests for a while. Maybe this winter.
Think I'll use full load for both coatings to try and keep things consistant. Life is complicated enough. Not a big fan of a lot of testing but it's a nessessary evil I guess.
I did some testing over the weekend regarding this question. My results are nothing but preliminary, but I thought you might get some use from the information.
I tested cutting the first coat with 50% H2O vs. a straight full strength coat. The second coat was full strength in both cases.
First, the paper seemed to absorb the 50% solution faster, so I ended up putting in a little more than 50% water, so that there was enough solution to enable consistant coating.
It appeared that I got comparable dmax values with both, although I can't test that right now, as my densitometer needs a new PS. However, they looked very similar in dmax.
I noticed that the 50% first coat seemed to result in a faster printing solution. I would guess that it printed 2/3 or 3/4 of a stop faster than the full strength solution.
The 50% coat also appeared to have a slightly smoother tone in the middle zones where it is most apparent. This could have been a coating varialbe, or it could be a product of the solution.
At this point, I don't see any drawbaaks to cutting the first coat with 50% water, and I'm inclined to think it may be a good thing to do, especially when printing larger, as it does result in a good bit of metals savings.
More tests are needed to determine if this is definately a win-win situation, but it appears to work well at first glimpse. Another test that might be worthwhile is to use a 1% oxalic acid solution instead of H2O for the first coat, and see if that improves that coating.
It may be possible to cut the solution strength of the first coat even further and still have the benefits of double coating, but I don't know how far that can go.
Just wondering if you think that using the diluted two coating method would have any adverse effects when working in in a higher humidity environment of over 80% or is this a non-issue. Also do you happen to know if there are papers that are better suited to high humidity.
Using two coats will probably increase DMAX of most papers, although some don't take too well to the second coat, and have problems with blotchiness.
I have speculated that there are several things going on here:
1. There is more sensitized material in the paper, which will result in a higher DMAX. By doing two coats, you are able to get much more material into the paper fibers than would be possible in a single coat, because some of the materials are at saturation in the mix.
2. The first coat is somewhat acidic, which helps prep the paper for the second coat.
3. The first coat is wet, which helps make the paper locally more humid, which helps with the second coating. I never blow dry after the first coat for this reason.
4. The first coat starts to work on the sizing in the paper, which makes it more absorbant to the second coat. For this reason, I think that the first coat is important, but not necessarily solely because of the metal salts in the coating. That;s why a pure H2O presoak may be beneficial in the same manner, but I suspect it will not get the DMAX improvement that a two metal salt coat print will achieve.
Typically, high humidity is not as big of a problem as low humidity to my understanding. I have printed up to about 70-75% and it seems to work equally well, although there is more of a printing out image, which will affect both the speed and the contrast. I try to keep my RH between 40 and 60%, and this is not too difficult except in the heat of the summer.
I don't have any real experience with high humidity levels, so I can't really recommend a specific paper to overcome any printing problems you may have.
I think the biggest problem you may have is getting the paper to dry in a reasonable amount of time. At that high humidity level, you would probably have to help the paper dry to avoid fogging and real long wait times. I think it would be important that you don't dry it too much after the first coat, however.