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Here are some general facts regarding emulsions that may help:
1. You don't mention what you are using to expose and for how long. Emulsion companies base their exposure times on tests done on a 5,000 watt multi spectral lamp. So if you are using a: a 500watt shop lamp or b: a DIY exposure system, or an entry level exposure system your times will be far longer than what the Technical data sheet indicates.
2. You also don't mention how you are imaging your art. From your post you are doubling the image so you are either using vellum or transparencies. If vellum try some toner enhancer to improve d-max (the blackness and opacity of the image).
3. When some areas don't wash out they are either: getting exposed in storage or your emulsion is past shelf life, but you say you mixed a new quart. How old was the diazo? Was it ever exposed to high temps for a day or more? Diazo can dark harden. Typically this makes it difficult to wash out images. Always store your diazo in the freezer if possible to preserve sensitivity, or make sure to keep it below 80 degrees. Over 80 degrees for long periods can ruin the diazo.

If you take a white rag and wipe the inside of the screen during development when it is wet do you see any emulsion color? If so you are underexposing the emulsion. However, if you use vellum or transparency you may be unable to increase exposure since the light is burning through the black areas and locking in the emulsion.

My guess is the screen is getting partially exposed. Do you develop your screens in a light safe area? Wash out should be done under yellow safety light. If you have any reflected sunlight in your washout area it can expose the screen as well. Washing out your screen outside in the shade will also be an issue.

Here is a link to determine your proper exposure time:
[media]http://www.murakamiscreen.com/documents/StepTestInstructions.pdf[/media]If you want you can post your exposure unit/film type/exposure time/emulsion for me to help further.

Alan Buffington
Murakami Screen
 
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