Restoring a Meyer window

I received an inquiry about restoring a Meyer window. The restorer said he would be using Lambert's glass and had access to Reusche and Keracolor stains. These are the images he sent, scroll down for my reply:

MY REPLY: Looking at your images I wanted to first say that not everything is silver stain. Forgive me if you already know this but only the ornamentation in the diamond quarries is silver stain. The yellow brown tone that appears to be fading off is some other pigment. I have attached a photo with some arrows below.

Not everything is stain.

Silver stain is very permanent as it is absorbed into the glass itself and not subject to corrosion from atmospheric weathering like vitreous pigments are.

As to the silver stain, I made many tests as I was preparing my book on stains. Here is a photo of my test on Lamberts glass: 

My tests on Lamberts Glass

I think you will have the best results with Reusche 1383 or Keracolor using a mixture of 1 part 76050 to 4 parts 73028/A. You will need to experiment to get the density of the application correct. Prepare two identical samples with a heavy to thin gradation application on Lamberts glass. Fire one sample and then you can compare the results to the unfired stain. Stains look radically different after they are fired so a fired/unfired sample is extremely beneficial. You can mix the stain with any medium but using oil may allow you to make a more controlled gradation. Silver stain is best fired between 538C/1000F - 593C/1100F Try this schedule as a starting point:

90 min to 540C/1004F

10 min to 580C/1076F

Hold for 45 min

If the stain is too heavy after firing it can be lightened with a cotton swab dipped in hydrofluoric acid - use extreme caution when working with acid in this way.

If you plan to fire the stain several times - make a test for this as well - stains can intensify during successive firings. I had a stain appear to "not take" once I washed off the clay body (all stains are premixed with ochre/clay). I refired the piece - without reapplying stain and it came out beautifully. Even knowing as much as I do - stains can remain a mystery :)! My best advice is to test, test, test and keep a good log - be scientific in your approach.

Metaling of Silver Stain

Silver stain is prone to an effect called “metaling” which occurs as an oxidation on the surface of the glass. It is characterized by a milky opalescence which can have a blue, green or brown cast. It is visible in reflected light. In transmitted light the stain will still appear yellow but with a reduction in transparency. Metaling can be unsightly and can only be removed from the surface of the glass by abrasion or with hydrofluoric acid. The cause of metaling is linked to temperature; the higher the stain is fired the more likely it is to occur. The chemistry of the stain, the chemistry of the glass and the thickness of application also play a role. Some stains are formulated with the addition of copper sulfate to intensify their potency. These are more likely to metal. Of the test samples the amber stains exhibited metaling, although not in the range of their thinner application.

Temperature Test - Color Follows Ion Exchange

The final test of my study demonstrates a chemical reaction described by W. A. Weyl, Coloured Glasses, ISBN 0-900682-06-X. He states that the surface exchange of silver ions with sodium ions in the glass begins at 752°F, but crystals of silver atoms, which transmit yellow light, don't form until higher temperatures are reached. Basically, the silver penetrates the glass even before we see any change in color. In this test 2 samples of glass were fired to 800°F and held at temperature for 20 minutes. The clay body of the stain was washed off and one sample was fired again to 1050°F and held for 2 hours. The upper tiles are the tin side of float and the lower tiles are Lamberts. Comparing these results with the previous test (which was also fired to 1050°F) reveals the role the clay body plays in the reaction. The purpose of the clay or ochre binder, besides suspending the silver oxide,  is to capture the resulting sodium salt, forcing more of the sodium ions present in the glass to exchange with silver.

REUSCHE 292465 (Amber H465)

REUSCHE 1382 (Orange #2)

REUSCHE 1384 (Yellow #3)

Temperature Tests - Multiple Firings

The object of this test was to discover what happens when glass which has already been stained is fired a second time. The upper sample is the tin side of float glass; the lower sample is Lamberts. Two pieces of each glass were to 1050°F and held for 2 hours. After cooling the clay body of the stain was removed and the right hand sample was fired a second time and held for 1 hour. The effect is subtle but the stain continues to disperse into the glass.

REUSCHE 292465 (Amber H465)

REUSCHE 1382 (Orange #2)

REUSCHE 1384 (Yellow #3)

Temperature Test - Hold Time

Firing slower or holding for a longer time at temperature will also have an effect. These samples were fired to 1000°F. The left sample was held for 20 minutes; the right was held for 6 hours.

REUSCHE D292465 (Amber H465) on Float (Tin side)

REUSCHE D292465 (Amber H465) on LAMBERTS

REUSCHE 1383 (Orange #2) on Float (Tin side)

REUSCHE 1383 (Orange #2) on LAMBERTS

REUSCHE 1384 (Yellow #3) on Float (Tin side)

REUSCHE 1384 (Yellow #3) on LAMBERTS

The Temperature Tests

In the next round of testing I selected 3 stains and made samples fired at 100° F increments from 800° F to 1400°F. The kiln was held at the temperature indicated for 20 minutes. This test reveals how temperature effects the silver stain reaction. The sweet spot appears to take place between 1000° F & 1100°F. In the images below, the upper row of tiles are the tin side of float glass and the lower row are Lambert's glass. The first tile in each group was left unfired. At temperatures above 1300°F the clay body in the stain began to fuse to the glass which accounts for the dark tiles. None of the 1400°F tiles are transparent as the clay body could not be removed. The additional tiles in the 1000°F range are discussed in the next entry.

REUSCHE D292465 (Amber H465)

REUSCHE 1383 (Orange #2)

REUSCHE 1384 (Yellow#3)

Glass Chemistry & Silver Stain

It was interesting to note that some glasses, like GNA were difficult to stain whereas the tin side of float glass and Bullseye’s “Reactive Ice” were extremely sensitive to the stain. The notes in one text I studied suggested that clear glasses with a blue or green cast would stain better than those with a yellow cast. Another mentioned that clarifying agents added to make glass optically clearer can inhibit the stain. This may explain why historic glasses, which were less “pure”, took the stain better. Of the 3 mouth blown glasses I tested, the glass coming from Poland achieved the best color range. Bullseye’s “Reactive Ice”, mentioned above, is a glass used by fusers that has been formulated to react with other glasses containing silver or copper. It takes stain extremely well, if you can overlook its double-rolled texture.

BULLSEYE Clear fusible

BULLSEYE "Reactive Ice"

Float Glass (non-tin side)

Float Glass (tin-side)

Desag/Schott GNA

KRASNOW 

LAMBERTS

ST. JUST

SPECTRUM "System 96"

SPECTRUM "Waterglass"

The KERACOLOR Stains

KERACOLOR 73028/A

KERACOLOR 76050

The OSTER Stains

OSTER Ancient Lemon

OSTER Ancient Winchester

OSTER Ancient Walpole

The REUSCHE Stains

REUSCHE 1382 (Orange #1)

REUSCHE 1383 (Orange #2)

REUSCHE 1384 (Yellow #3)

REUSCHE 1388 (Orange Intense)

REUSCHE 1390 (Amber Intense)

REUSCHE D292465 (Amber H465)

The DEBITUS Stains

DEBITUS 20% Silver Chloride

DEBITUS 40% Silver Chloride

DEBITUS Amber

DEBITUS 10% Silver Chloride

DEBITUS 20% Silver Chloride

DEBITUS 40% Silver Chloride