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black japan gremlins
Posted by: drew ()
Date: September 29, 2011 01:16PM

Japanning tins this week is giving me a headache, but it's not from the mineral spirit fumes.

As you'll see in these photos, my second coat appears to be eating at the base coat and causing this sort of sagging, tearing appearance. This is happening almost immediately after pouring the second coat. This is using John Coffer's most recent recipes (Spar Urethane in coat 1; Canada Balsam in coat 2) and baking at his recommended temperatures (300ºF for coat 1; 225ºF for coat 2).

I've tried:
    [*] Making a new, thicker batch of second coat japan. i.e., cooking it longer, hotter. (Reasoning: perhaps the second coat ingredients weren't dissolved well enough and the proportion of mineral spirits was too high.)
    [*] Letting the plates dry for about two hours after first coat application prior to baking. (Reasoning: perhaps the plates weren't cured enough before baking)
    [*] Letting the plates sit overnight after first coat baking before applying second coat mixture. (Reasoning: perhaps the plates weren't cured enough after baking)


Next on my list would be to try mixing a new batch of first coat japan and cooking it longer and hotter, thinking perhaps it is too thin. But, while I cook and recoat, I wanted to get some thoughts from the experienced japanners out there.




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Re: black japan gremlins
Posted by: Ty G ()
Date: September 29, 2011 02:51PM

Yup, seen that gobs of times. Still have it happen rarely. Your problem is not between the two coats, it is prior to the first coat. Here is what I narrowed down the cause to; two solutions.
-Use a rough grit green scotch-brite pad to "roughen" up the metal prior to first coat. Then wipe with mineral spirits to clean off metal particulate stuff.
-Make SURE to let all mineral spirits evaporate off the metal before dipping, or whatever method you use. This can take 15 minutes for the MS to evaporate completely; and I am in Texas.

Don't cook hotter and longer. That will just give you pretty cracks and peeling.
No, it is not too thin.
The "sheen" and thickness of the japan looks great to me.

Another note, since I only do plates for myself and not that many or large; I just use the balsam mix for both coats. Still do the two different temps. I find it more user friendly to just have to deal with heating and keeping up with one solution. Have not noticed any difference.

www.guillorycameras.com



Edited 1 time(s). Last edit at 09/29/2011 02:55PM by Ty G.

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Re: black japan gremlins
Posted by: drew ()
Date: September 29, 2011 03:03PM

Ty,
Thanks so much. I was pretty happy with the appearance of the japan, myself. In fact, my first two batches came out beautifully, but they were mostly quarter plates. I really started to notice the issue on the next batch, which included half plates and 5x7s, but in my last batch, it happening even on the quarters.

I was using #00 steel wool to roughen up the plates, followed by a wipe-down with mineral spirits.

I'm going to give your solutions a try. I'll pick up a green Scotch Brite pad in town today, if we don't have one under the kitchen sink already. And I'll lengthen my pre-bake drying time. (I'm flowing the stuff on.) Here in West Virginia, our humidity is pretty high. I'll double my drying time from 2 hours to four hours and see if that helps, on this next batch.

For the ones where the sags aren't as pronounced, I thought I might give them another top coating and see if they can be salvaged.

It might sound silly, but at this early stage in making the plate, watching the second coat do this to the first almost as heartbreaking as having your varnish eat your collodion.


Nothing like a little pressure to get this right... I have an event this Saturday. smiling smiley

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Re: black japan gremlins
Posted by: Ty G ()
Date: September 29, 2011 04:12PM

Don't really need to do the time thing for the drying after cleaning with mineral spirits. I use paper towel to clean plate with mineral spirits, then use an old T-shirt to sort of wipe the plates of the m.spirits. Then, you can simply look at the plates in reflected light and see the un-evaporated m.spirits. Make sure to check the backside for un-evaported m.s. as well, the lack of ventilation from leaning the plates up against something makes the back evaporate slower.

Another thing I do to make this easier is I have a pyrex dish and I pour the japaning into the dish, and using latex glove, I just dip the plates. Makes it fast and you have the option of either side to use. I had found that by the time I flowed all my 15 or so plates in the batch, the first one was much dryer than the last and this did affect my end results. Dipping is fast, easy, and it keeps things consistent. I dip for both coats.

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Re: black japan gremlins
Posted by: drew ()
Date: September 29, 2011 04:17PM

Sorry; perhaps I wasn't clear. The increased drying time I'm referring to is between flowing on the first coat of japan and baking for the first time.

Thanks also for the tip about dipping versus flowing.

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Re: black japan gremlins
Posted by: Ty G ()
Date: September 29, 2011 05:01PM

Drew, don't time that either. It can vary too much! When the plates are mostly dry to touch, but have a small wet spot still at the bottom, put them in the oven. I have a paper towel and dab the last little bit of wet on the bottom edge as I put them into the oven. Watch John's video, the plate is mostly dry and he wipes the drip edge with a towel as putting them into the oven. This time is around 5 to 15 minutes from dipping.

Feel free to give me a call today if you need; I am not really doing anything today. I'm stuck waiting on woodwork supplies before I can continue with work; well, also I've got bottle-feeding sessions mixed in. 903-520-0713

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Re: black japan gremlins
Posted by: drew ()
Date: June 09, 2012 12:58AM

Sorry to resurrect a somewhat stale thread, but I thought I'd tie this one up with a conclusion. I've baked many batches of plates in the months since I came across the original problem noted in this thread last fall. I have since switched to the cold-rolled shim stock available from McMaster-Carr (both in roll and sheet form) and the problem has disappeared. Comparing the McMaster stock side-by-side with the metal I was using from a local supply house, I can say that the local stuff has a much heavier coating of oil. In fact, it's more like grease compared to the light oil used on the McMaster shim stock. My conclusion is that I simply wasn't thorough enough in getting the heavy oil/grease off of the local stock, which led to the finish problems I encountered. On the local stuff, I tried using mineral spirits, and even acetone (per Todd's advice), but met with the same results. However, mineral spirits seem to work just fine for cleaning up the McMaster stock.

Thanks to Ty and to Todd for their help in troubleshooting this issue. In addition to helping me narrow down the potential cause of the problem, their guidance has helped me become a better, more consistent japanner.

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Re: black japan gremlins
Posted by: RobertSzabo ()
Date: June 11, 2012 03:54PM

Thanks for the update on this Drew. It may help someone else in the future.

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