Richeson Magic Brush technique

[Bob Fukura]

Hi, all:

I've been using the Richeson 9010 brush for a while now (having been introduced to it through a great workshop with the wonderful Kerik Kouklis) and have some questions on technique that I hope more experienced folks can help with. I'm doing Pt/Pd printing on COT 320 and use a 2 inch brush.

I've read many posts in the past from others about using it wet, shaking it 'til the excess is gone (but no separation in the bristles) and going left to right and up and down, etc. On an 8x10 COT 320, I'm using 18 drops FO + 14 Pd + 4 Pd for each of 2 separate coats--the 1st is diluted with water (so total volume is still 36 drops per coat). My problem is knowing when to stop brushing--It seems to take a long time before the amount of liquid I'm pushing around decreases to where I can absorb the leftover with the edge of a paper towel (I've brushed as long as 12+ min. or so sometimes). This often leads to fine white lines on the final print, which I believe is from abrasion. My darkroom is at 55%RH via a humidifier and I pre-humidify each sheet before coating for about a minute or so a few inches from the humidifier's nozzle.

Is this normal behavior for the brush or am I doing something wrong? Can someone give me a rough idea of how long I should be pushing the sensitizer around before I call it quits and soak up the rest with a paper towel? Or should I be using less sensitizer? Thanks for you help!

Bob

 

[Mateo]

I don't think I'm being stingy with the metals but my drop count is way less than 36 for an 8x10!

 

[Kerik]

Hi Bob!! Glad to see you on APUG. Thanks for the kind words...

Wow... 12 minutes?? You're going to get carpal tunnel syndrome! You're not that far off compared to the volumes I use, but clearly you have more than you need. Start by cutting back on the sensitizer by 25 or 30%. You should be done brushing in a minute or 2.

 

[Bob Fukura]

Hi, Kerik:

I was hoping you'd respond!!

Anyway, I tried cutting down the drop count to 24 drops total before and it seemed to lessen the time for coating by quite a bit but the Dmax I was getting was a bit less than the higher drop count. I'm beginning to think that Dmax may not entirely be related to drop count, however, and maybe a faster coat may yield a good Dmax by not wasting time working the sensitizer deeper into the paper with prolonged brushing. I'll try this again with a shorter coating time. Thanks for your help.

Mateo, I think you echo Kerik's comments but somewhere I read people were using 2ml sensitizer per 8x10--with 20 drops per ml, I thought that would be 40 drops per 8x10 sheet.

Bob

 

[TheFlyingCamera]

Hi, Kerik:

I was hoping you'd respond!!

Anyway, I tried cutting down the drop count to 24 drops total before and it seemed to lessen the time for coating by quite a bit but the Dmax I was getting was a bit less than the higher drop count. I'm beginning to think that Dmax may not entirely be related to drop count, however, and maybe a faster coat may yield a good Dmax by not wasting time working the sensitizer deeper into the paper with prolonged brushing. I'll try this again with a shorter coating time. Thanks for your help.

Mateo, I think you echo Kerik's comments but somewhere I read people were using 2ml sensitizer per 8x10--with 20 drops per ml, I thought that would be 40 drops per 8x10 sheet.

Bob

Bob- I'm not the expert that Kerik is ( I just follow the Bostick & Sullivan directions for mixing my emulsion), but I have usually more than enough to cover an 8x10 using 18-20 drops of sensitizer and Pd each, so between 36-40 total drops, and that gives me great dmax. It usually takes me 1 minute of brushing to get my chems absorbed. I don't pre-humidify my paper however.

 

[Bob Fukura]

Bob- I'm not the expert that Kerik is ( I just follow the Bostick & Sullivan directions for mixing my emulsion), but I have usually more than enough to cover an 8x10 using 18-20 drops of sensitizer and Pd each, so between 36-40 total drops, and that gives me great dmax. It usually takes me 1 minute of brushing to get my chems absorbed. I don't pre-humidify my paper however.

Hmmmm... It seems like you're using a similar drop count that I'm using but my sensitizer seems to take longer to absorb (assuming you're also using COT 320). Maybe my darkroom is too humid (my hygrometer is perhaps wrong) to prevent enough evaporation of water from the sensitizer during coating. Do you know what Relative Humidity your environment is at? Do you have much excess sensitizer after your coating or is it all absorbed after the minute?

Thanks for your input!

Bob

 

[TheFlyingCamera]

Hmmmm... It seems like you're using a similar drop count that I'm using but my sensitizer seems to take longer to absorb (assuming you're also using COT 320). Maybe my darkroom is too humid (my hygrometer is perhaps wrong) to prevent enough evaporation of water from the sensitizer during coating. Do you know what Relative Humidity your environment is at? Do you have much excess sensitizer after your coating or is it all absorbed after the minute?

Thanks for your input!

Bob

I don't know the relative humidity of my darkroom other than to say it is certainly less than yours. I have NO leftover solution at the end of the minute. I am coating on COT 320. I would venture to say that the room humidity is around 30-35%. I also do not pre-humidify my paper.

 

[Joe Lipka]

You are coating the smooth side of the paper of course...

 

[Wayne]

. I would venture to say that the room humidity is around 30-35%. I also do not pre-humidify my paper.

Unless you are doing something to intentionally dehumidify, or running forced air heat in the middle of an arctic cold blast, that would be an extremely low RH. My house doesnt even get that low under the latter circumstance, rarely dipping below 40% which still causes me to have dry skin, sore throat, etc. Normal for non-desert mid-latitudes would be closer to 50-60%.


Wayne

 

[TheFlyingCamera]

Well, then I have no idea what the actual relative humidity is. All I know is that the humidifier in my bedroom tells me when I leave it off during the day that the room RH is in the 20s to low 30s. I do have forced air heat in the house. And it is still wintertime here more or less. Either the humidifier's sensor is, for lack of a better term, dorked up, or I just have a very high tolerance for dry houses.

 

[Jim Noel]

If the RH ever got to 50% in my darkroom I would be adding to it with perspiration. It is usually in the 20-30% range, but can get down to 10% or less in certain weather conditions.

I normally do not re-humidify, but when the RH is extremely low, I do so over a small electric skillet with water almost simmering. Of course this also raises the RH in the general room atmosphere.

 

[Bob Fukura]

You are coating the smooth side of the paper of course...

Hi, Joe:

Yes, I am coating on the smooth side.

Anyway, one other factor I'm thinking about may be playing a role with my problem. My basement darkroom temperature is a rather chilly 62 - 64 deg. F. Perhaps this is inhibiting the absorption/evaporation of sensitizer despite the RH being 55%. I notice that after any of my coats are applied, it takes about 10 min. before the "wet look" goes to satiny/velvet/matte look when I start to blow dry it. Most sources I've looked at say it usually takes 5 min. or less to reach the satin look so maybe my cold darkroom temp. is playing a role here. I always thought the RH determines the rate of evaporation but maybe temperature plays an important role also. Any weatherman (weatherperson) or physics person out there who can comment on this?

Thanks for all your input--It's nice to hear what other people are doing about what I believe is an overlooked problem with hand coating.

Bob

 

[Kerik]

Bob,

I would definitely try to warm up your darkroom space a bit. Or, coat the paper elsewhere in the house where it is warmer.

 

[Wayne]

Hi, Joe:

I always thought the RH determines the rate of evaporation but maybe temperature plays an important role also. Any weatherman (weatherperson) or physics person out there who can comment on this?

Bob

No, but I aced a course in meterology 25 years ago. I've just been dying to use it!

Yes, temperature will have such an effect. Cooler air cannot hold as much moisture as warm air, (hence the relative in relative humidity) and will slow evaporation.


Wayne

 

[Bob Fukura]

Kerik:

I'm definitely going to warm up my darkroom--I think this will help with the coating. Thanks again for your help!


Wayne:

I'm thinking both the RH and the ambient temperature play a role here. Interestingly, in my search for the relationship, I found this helpful site:
http://www.shorstmeyer.com/wxfaqs/humidity/humidity.html
Thanks for your input!

Bob

 

[Kimberly Anderson]

I coat my papers in the main floor of my home, let them dry there then take them into the basement where I have my plate-burner. The basement is unheated and uninsulated and is a constant 56 degrees. I have wondered if temperature affects the coating/drying process...guess we have a good answer now.

BTW, I do the processing in the main level of the home too.