Shards of Indiana, Pennsylvania - A Second Look - by Jerry & Cleo Kudlac

Non-transparent Glass Samples

Northwood (1896-1899) and Dugan/Diamond made several kinds of non-transparent glass such as opaque (alabaster, custard, turquoise), opalescent (cranberry, clear, blue, green, vaseline, etc.) and black glass.  Some carnival glass patterns were first produced in non-transparent glass; then later in opalescent glass, followed by Peach Opal carnival glass.  In this section we will describe the non-transparent glasses including end-of-the-day type of glass.

Opaque (6 different samples)  

An early 1878 patent referred to this kind of opaque glass as: fusible porcelain, alabaster, milk, cryolite, and opaline glass. Opaque glass usually does not transmit light and is considered more fragile than transparent glass.  This type of glass was made by the addition of white clay (kaolin) or similar compounds known as opacifying agents (fluorspar, feldspar, kryolith and tin oxide) to transparent glass which resulted in a milky-white or semi-transparent glass on melting and did not require reheating to develop the opaque white appearance.(15A).  Northwood introduced Ivory glass about 1899 with the Pagoda pattern, now know as Chrysanthemum Sprig.  The Ivory or custard glass had a light yellow appearance due to uranium oxide in the glass which glows very bright under a black light (15-B).  Dugan modified Northwood’s Ivory formula by reducing the amount of uranium by about 50%, replacing lime with lead and adding fluorspar and/or feldspar.  This resulted in a somewhat lighter yellow color Ivory and one that glows with less intensity under a black light (15C).  

F.S. Shirley received a patent in 1885 for a white opaque glass and a colored opaque glass by adding colorants (copper and/or gold).  This patent was probably a source of information used by Northwood and Dugan in the development of their opaque colored glass such as turquoise (15-D) and pink slag (15-E).   In 1900, Bastow and Dugan, experimented with a pink slag glass with Dugan being credited for working out the final formula.  The Inverted Fan and Feather pattern was made in the pink slag, but the pink slag was not popular at the time; and today, this pattern in Dugan’s pink slag is difficult to find and usually commands a good price

Though not an opaque glass in glassmakers’ terms, black glass is included here since it does not transmit light (15F). Black glass appears opaque due to the large amounts of manganese used in its manufacture. Nickel, chrome and cobalt colorants were probably added as well.  Thin fragments of this glass, when viewed in sunlight, have a deep dark purple appearance typical of dark amethyst glass made with manganese.  Black glass was introduced by Diamond in 1924 and produced through 1930.  Items made in black glass were base plates for bowls along with consoles sets and vases with gold and silver decorations. A few iridized and non-iridized carnival glass patterns have been found in black glass.  Several other opaque glass samples are shown in the section: “Miscellaneous and End-Of-the-Day Glass”.

Shown in photograph 16 are: Intaglio berry sauce in Ivory or custard)-16A, Inverted Fan and Feather Tumbler in Pink slag-16B, Chrysanthemum Sprig Tumbler in turquoise-16C, and Windflower bowl in non-iridized black glass-16D.

Opalescent (heat sensitive glass - 4 samples)

This type of non-transparent glass is considered to be a “Striking Opal” glass which means that it was heat sensitive and required cooling, then re-heating to develop the opaque white appearance. Opalescent glass was made by adding bone ash or calcium phosphate to transparent glass which was transparent on melting.  The molten glass was gathered, shaped or pressed; specific parts of the pattern were cooled with a blast of air allowing the bone ash to crystallize; then upon reheating, the cooled part of the glass would strike (become opalescent or opaque white on a clear or colored background).  A patent describing this process was issued in 1886. Shown in photograph 17 are: Blue glass-17A, Gold-ruby (Cranberry) cased-17B, Clear-17C, and Vaseline-17D, each color having a white opaque pattern.

Three kinds of striking opal glass were made at the Indiana plant.  The first kind of striking opal was cased opalescent glass which was described in several patents issued in 1886.  Northwood introduced cased opalescent glass about 1896-1899.  Clear, opaque or colored glass was cased (a very thin layer) with the bone-ash glass.  Sometimes two, three or four layers were used: clear, ruby-gold (two layers) and opalescent.  The cased glass was blown into a mold to impart, not only the shape; but also, to impress a raised pattern in the outer glass layer containing the bone ash.  After removing from the mold, the outside of the item was cooled with a blast of air causing the raised pattern to cool more rapidly than the body of the glass. This cooling crystallized the bone ash in the outer raised pattern; which upon re-heating, would strike the white opaque pattern on a colored or clear background.  Gold-ruby glass was referred to as cranberry opalescent.  Examples of opalescent patterns found in cased opalescent glass are Daffodils, Swastika, Coin Spot and Spanish Lace (Brocade) on clear, red, blue, green or yellow colored glass.  See photograph 18 - Blue Daisy and Fern Water Pitcher and tumbler.

The second type of striking opal was “pressed” transparent or colored glass containing the bone ash. After the glass was pressed, the raised parts of the patterns were cooled with a blast of air and re-heated to strike the opal in the pressed pattern or edges.  This type of opalescent glass was advertised in the Sommers catalog from 1906-1909.  A number of carnival glass patterns were made in this type of glass.  Colorants such as chrome (green), uranium (yellow), copper (blue), and manganese (amethyst), etc. were added to transparent glass creating the different base or background colors.  Shown in photograph 19A is Dugan’s Daisy and Plume in blue (note the holes in feet); in 19B is an Alaska Berry Bowl in Vaseline Opal.

The third type of striking opal is known by carnival collectors as “Peach Opal” and was retailed as a higher price because of the difficulty in making a glass that was both opalescent (opaque) and iridescent. The exact method of iridizing the opalescent glass is not know, but the process is speculated to be as follows:  Molten clear glass containing bone ash was pressed into the desired shape; removed from the mold, specific parts of the glass was cooled with a blast of air to allow the bone ash to crystallized; then sprayed with the iridizing solution (example ferric chloride), and finally re-fired to develop both the marigold iridescent color and to strike the opal.  The opal may appear on the raised parts of the pattern and/or on the outside edges (from ¼ to 3 inches) on bowls, plates, vases, etc. The remaining part of the glass would be transparent clear glass with an iridized marigold surface.  Some examples of Peach Opal carnival glass were not iridized on the back side.  Dugan is generally regarded as having made the best quality Peach Opal carnival glass.

Granite and Splatter Ware (6 samples)

Granite ware was one of Dugan’s first iridescent lines that appeared about 1905-1906 and is also found in non-iridized glass.  The basic soda/lime clear or colored molten glass was gathered on a blowpipe, rolled in various colors of glass frit (powdered or ground glass); blown into a spot mold (if a pattern is desired), then blown into its final shape in second mold.  For iridescence granite ware the glass was probably sprayed or fumed with tin chloride and reheated to develop the iridescence and fuse the frit onto the glass surface.  Various colors of Granite ware appeared about 1900-1902; others are mentioned in Butler Brothers catalog in 1905, and may be related to the Japanese, Pompeian and Venetian vases.  Shards of six colors of Granite ware are shown in photograph 21-A (Clear, Green, Light blue, cobalt blue, ruby-gold, and Vaseline.  

Splatter glass (spangled glass) was similar to granite ware, but instead of rolling the molten glass in glass frit it was rolled in colored glass flakes and then re-fired to fuse the flakes to the glass surface, a process that was patented in 1884.  After the glass was formed, the outside of the item (example tumbler) was treated in a hydrofluoric acid solution to give it a satin finish.  Northwood had several lines of mold blown splatter glass in various colors. An example of a shard of yellow spatter glass is shown in photograph 21B.

Miscellaneous and/or End-Of-the-Day Glass (16 samples)

Most of the samples shown in the following photographs were probably a mixture (slag) of glasses that was discarded at the end of the day.  A few pieces of carnival glass have been reported in a “slag” glass, but they are very rare and unusual.  Note: The word “glow” used in the photos below indicates the glass shard glows under a black light.

Photograph  #23:   A –blue green glass, glows;  B – aqua green, glows; C- blue and clear glass, D- light green, brilliant glow.

Photograph  #24:  A- Orange red and yellow opaque slag - similar to Northwood Chinese Coral,  B- light green and opal, glows; C-Translucent blue green, glows; D- Aqua with opal, faint glow.

Photograph #25:  A- Red glass, B- Translucent light green, glows; C- Orange (glows) with yellow layer, D- Opaque yellow

Photograph # 26: A- Light blue and layers of opal, glows; B- Green with white opal, C- Opaque yellow with red, D- Stone with layer of cobalt blue glass, E- Stone probably from melting pot.

The melting pots or tanks used to melt glass were made of a specific type of low iron clay to minimize a color change in the glass by the iron.  A number of secondary industries specialized in making melting pots and tanks of various sizes for the glass industry. Many patents for improvements in pot and furnace construction were issued during this time.  Smaller factories used single batch furnaces that allowed them to produce a variety of glasses and colors.  Glass batches would usually melt in 22 to 26 hours at about 2400 - 2600 degrees F.  The glass was used from a day to a week or more depending on the need for that type of glass.  Glass melting pots and furnaces were always keep at high temperatures of 1500-2500 degrees F. and never allowed to cool down.   Glass cullet (recycled crushed glass) was used to facilitate melting and to slow the erosion of the pots, but the high temperature and alkali of the glass melt eventually eroded the clay pots.  As a result of the erosion, small particles of the clay would break off and become mixed into the glass melt. Occasionally, black or grey clay particles can be found in Carnival glass.  The stones in photograph (26-D & E) were probably from a clay pot that had failed and had to be replaced

This section concludes the types of glass shards found at the Indiana PA., glass dump.  See the final section of this series that covers the identified  shard patterns .