The Bostick & Sullivan Carbon Study Group

Things New to Us About Carbon Printing

We are in the early stages of the carbon renaissance. Every day we learn something new. Here is where new things we have learned about carbon printing will be posted until the second edition of the book is published. Carbon has lots of variables so we are not always absolutely sure that the recommendations here are 100% correct, but at least, its a starting point for a cure to a problem.

Readers are encouraged to send  E-mail to richsul@earthlink.net and share your findings. I want to thank my compatriots in the Carbon Study Group: Gordon Mark, Carol Becvarik, Howard Efner, and Molly Bass for their help.

 

 

Washing Yupo before use

It appears that Yupo every once in a while will shed the image and it will shed rather radically. Gordon noticed that when an images shed, that after he washed the Yupo in bleach and rinsed in hot water so he could reuse the Yupo, the sheet held better to the image. We are now washing even new sheets of Yupo in bleach and then rinsing in hot water before reuse. There is probably a film of release agent that can cause problems and can be washed off.  Cascade dish washing detergent appears to work as well. Cascade is a mild alkali and it doesn’t foam much. I suspect any detergent will work just as well.

 

Mid tone safe edge

Most of the earlier classic books on carbon printing suggest putting a opaque or black safe edge on the negative. This works OK in most cases but if you have some black edges on your print you may find them flagging during development because the black safe edge left a pure white margin on the edge of the image area. We have found that a gray edge works best as it adheres to the support and tends to protect the image. If you are making digital negs just add a mid tone margin in Photoshop. If you are using tape on your negative  for a safe edge ordinary masking or artist or drafting tape is partially transparent and will leave a gray edge.

 

Brush sizing art paper for a support.

Dip sizing paper in a tray of gelatin is messy. We now use a foam brush for sizing.

Make a 3% to 5% solution of 250 Bloom gelatin. Smooth hard papers may need the lower amount while rough absorbant paper may need the upper amount or even more.

To make the gel solution add 30 gm of 250 Bloom Gelatin to 1000 ml of cold water. Wait 1/2 hour while it swells and then heat in a double boiler or small crack pot until dissolved. Now add 3 gm of potassium alum per liter of the the gelatin. Tape the corners of the paper to a flat surface and with a foam brush coat with warm gelatin. Let dry and do a second coat. A clip on lamp with raking light coming towards you will help you see where you are coating. For large sheets of paper a 4 inch brush is good.

Allowthe paper to dry thoroughly. Before applying the second coat, buff with a piece of paper towel to remove any particles adhering to the paper. They can cause spots in the prints. These could be paper pils drageed up by the brush or undissolved gelatin particles for some unknown reason.

Apply a second coat and allow to dry. Buff lightly with a paper towel before using.

A third coat may be necessary on very rough or course papers. Some earlier works on carbon printing say the paper hardens over a three day period. We find it is hard enough after it is dry after the second coat.

Sheddding and blistering

Having your print shed or blister during development is a problem that occurs at times. It almost seems to happen randomly. It is more common with sized art paper and to some degree with Yupo. It is less common with fixed out photo paper. Inkjet photo paper, due to the micropores, grabs on for dear life and almost never sheds. The problem with most inkjet papers is they are hard to clear and often leave a yellowish tint. (This is an area for further exploration for some experimetally minded printers)

One cure that appears to work in many cases is to extend the mating time. Many printers can get buy with a 20 minute mate. If you are getting shedding allow the mate to last for 1 hour. If that cures it then gradually back off on your time.

Another cure is to reduce the wet time prior to squeegee and mate. You may also reduce the temperature of the mating bath or some of both time and temperature. In most cases of shedding it has to do with a too warm or a too long mate. In some cases, though rarer, your wet time is too short. How do you tell which it is? Good question.