Tack Soldering

Tack soldering is the placing of a small amount of solder on the foil to hold two or more pieces together, so the main soldering can be performed without disturbing any placing of the remaining pieces.


The advantage of tack soldering is it can allow you to completely eliminate framing. You can just hold two pieces together with one hand and spot a dab of solder to hold them together. You don't have to do this for all pieces - just enough of the outside pieces to hold the whole project together. Once you've tack soldered, everything will be held in place and you can just run the beads without further considering the placing of the pieces.

For free form shapes, tack soldering is always quicker. You may want to use nails or tacks to hold all the glass in place while you tack solder.

With big foil projects or ones that have to fit into a predetermined dimension, tack soldering ensures there is no growth through movement of the pieces.

It's a quick way to avoid having to fiddle with each piece to make sure each is exactly lined up before starting with the running of the beads.

Soldering Bit Composition

Most bits are made of copper, which is suitable because of its excellent thermal conductivity and high heat content per volume. Some bits are plain copper, while others incorporate various additives or have a protective plating applied.

One of the most common problems associated with plain copper bits, is that tin-lead alloys (more specifically the tin in the alloy) will attack the copper, dissolving it away. This makes it necessary to continually file the bits to maintain the required shape, giving these bits a shortened working life. Another concern is the amount of impurity that is imparted to the solder joint when using bare copper bits.

Adding tellurium to the copper improves both wear and oxidation resistance, but does not protect the tip from rapid deterioration. It has been determined that both iron and nickel, despite their low conductivity, are wettable, offer a high level of resistance to erosion and their heat per volume is close to that of copper.

Because of these facts it is possible to maintain good conductivity, while increasing the erosion resistance by plating copper bits with either nickel or iron. These plated bits are generally referred to as nickel-clad, or iron-clad and make up a large majority of the bits in use for modern soldering applications.

Courtesy of American Beauty Tools

Even Solder Beads on Edges

Running an even bead on the edges of copper foiled projects is often difficult. Several things can help.

Hold the panel vertically and ensure the edge you are applying solder to is horizontal. This means that you have to keep moving anything that is not rectangular.

To apply solder and move the piece ideally needs three hands – one for the solder, one for the iron, and one to manipulate the piece. Failing such an evolutionary leap, you can use a small vice to continually alter the angle of the edge, you can get a friend or colleague to manipulate the panel, or you can place the solder so that you can pick up little drops of solder and place them on the edge. With practice, you can pick up some solder and transfer it to the edge before the previous dot of solder has cooled, so leaving a smooth bead by the joining of the dots.

Alternatively, you can place dots of solder near each other around the piece. You then come back and with one hand manipulating the piece the other can use the solderimg iron to heat and join the dots.

You do have to be careful that you do not move the panel before the solder has hardened, or it will run down the newly created slope to the new horizontal edge.

I find that it is much more difficult to run a bead on an edge than it is to “pat” the solder dots. This patting motion allows the solder to join together, but does not heat such a long line that it flows as you turn the piece to keep the edge currently being soldered horizontal.

Even Solder Beads

Getting even solder beads is a lot about where you look while you solder. Unlike drawing or cycling looking at where you are going is not so useful when soldering. You need to see the effects of what you are doing so looking behind the solder bit will help you understand what you are doing. If the bead begins to get small or narrow you either slow down the forward movement of the solder bit or add solder to it more quickly. If the bead begins to get too thick, you do the opposite. You can move the bit faster, or reduce the speed of feeding the solder to the bit.

Another element in getting an even bead is the heat being delivered. If you use a wide soldering bit you are delivering more heat to the joint. You hold the chisel bit so that it runs along the foil. The bigger the bit, the more heat is being held. And the more heat held in the bit, the more heat is applied to the soldering. Small bits are for getting into tight spots and for decorative soldering. Big wide bits are best for running beads.

Plaster Properties - Effect of Plaster-Water Ratio

Plaster-water ratio (by weight) of 100 plaster to 30 water gives:
a setting time of 1.75 mins,
a compression strength of 813 kg/sq cm., and
a density of 1806 kg/cubic metre

Plaster-water ratio (by weight) of 100 plaster to 40 water gives
a setting time of 3.25 mins,
a compression strength of 477 kg/sq cm., and
a density of 1548 kg/cubic metre

Plaster-water ratio (by weight) of 100 plaster to 50 water gives
a setting time of 5.25 mins,
a compression strength of 318 kg/sq cm., and
a density of 1352 kg/cubic metre

Plaster-water ratio (by weight) of 100 plaster to 60 water gives
a setting time of 7.24 mins,
a compression strength of 230kg/sq cm., and
a density of 1207 kg/cubic metre

Plaster-water ratio (by weight) of 100 plaster to 70 water gives
a setting time of 8.75 mins,
a compression strength of 176 kg/sq cm., and
a density of 1083 kg/cubic metre

Plaster-water ratio (by weight) of 100 plaster to 80 water gives
a setting time of 10.5 mins,
a compression strength of 127 kg/sq cm., and
a density of 990 kg/cubic metre

Plaster-water ratio (by weight) of 100 plaster to 90 water gives
a setting time of 12 mins,
a compression strength of 99 kg/sq cm., and
a density of 908 kg/cubic metre

Plaster-water ratio (by weight) of 100 plaster to 100 water gives
a setting time of 13.75 mins,
a compression strength of 70 kg/sq cm., and
a density of 867 kg/cubic metre

Properties of Typical Gypsum Plasters and Cements

No. 1 pottery plaster
Water to be added as % of dry mix by weight - 70%
Setting time - 27-37 mins
Dry density (kg/cubic metre) - 1106
% expansion on setting - 0.21
Compressive strength (kg/sq cm) - 127.26


No. 1 molding plaster
Water to be added as % of dry mix by weight - 70%
Setting time - 27-37 mins
Dry density (kg/cubic metre) - 1106
% expansion on setting - 0.20
Compressive strength (kg/sq cm) - 141

Plaster of Paris
Water to be added as % of dry mix by weight - 70%
Setting time - 27-37 mins
Dry density (kg/cubic metre) - 1106
% expansion on setting - 0.20
Compressive strength (kg/sq cm) - 141

No. 1 Casting plaster
Water to be added as % of dry mix by weight - 65%
Setting time - 27-37 mins
Dry density (kg/cubic metre) - 1162
% expansion on setting - 0.22
Compressive strength (kg/sq cm) - 170

Pottery plaster
Water to be added as % of dry mix by weight - 74%
Setting time - 27-37 mins
Dry density (kg/cubic metre) - 1057
% expansion on setting - 0.19
Compressive strength (kg/sq cm) - 127

Hydrocal cement
Water to be added as % of dry mix by weight - 45%
Setting time - 25-35 mins
Dry density (kg/cubic metre) - 1442
% expansion on setting - 0.39
Compressive strength (kg/sq cm) - 35

Hydroperm cement
Water to be added as % of dry mix by weight - 10%
Setting time - 12-19 mins
Dry density (kg/cubic metre) - <641
% expansion on setting - 0.14
Compressive strength (kg/sq cm) -


Hydro-Stone cement
Water to be added as % of dry mix by weight - 32%
Setting time - 17-20 mins
Dry density (kg/cubic metre) - 1914
% expansion on setting - 0.24
Compressive strength (kg/sq cm) - 707

Ultracal cement (30)
Water to be added as % of dry mix by weight - 38%
Setting time - 25-35 mins
Dry density (kg/cubic metre) - 1588
% expansion on setting - 0.08
Compressive strength (kg/sq cm) - 424

Solarisation

Old glass can show changes in colour as evidenced by the different colour of the glass under the lead came where the light cannot reach the glass.

Drew Anderson has provided the explanation.

This change in color of some glass is known as solarisation.

The main ingredient of most glasses is silica, which is usually introduced as a raw material in the form of sand. Silica itself is colorless in glass form but most sands contain iron as an impurity, and this gives a greenish tint to glass. By adding certain other ingredients to a molten glass, it is possible to change the greenish color and produce colorless glass.

These ingredients are known as decolorizers, and one of the most common is manganese dioxide (MnO2). In chemical terms, the manganese acts as an oxidizing agent and converts the iron from its reduced state - which is a strong greenish blue colorant - to an oxidized state which has a yellowish, but much less intense, color. In the course of the chemical reaction, the manganese goes into a chemically reduced state, which is virtually colorless.

When pieces of decolorized glass containing reduced manganese are exposed to ultraviolet radiation for long periods of time, the manganese may become photo-oxidized. This converts it back into an oxidized form. Even in low concentrations this imparts a pink or purplish color to glass. The ultraviolet rays of the sun can promote this process over a matter of a few years or decades.

Selenium and cerium have also occasionally been used as a decoloriser and can produce solarisation colors, just as manganese does. The colors developed by these two elements are said to range from yellow to amber.

Mesh Sizes from a Typical Manufacturer

Mesh sizes have traditionally been measured by the number of wires per square inch used to sieve the material. This table gives a grit size measurement for the mesh/grit numbers in common use.

Mesh = Mesh opening (mm)
12 =   1.5240
14 =   1.2954
20 =   0.8636
30 =   0.5156
40 =   0.3810
50 =   0.2794
60 =   0.2337
80 =   0.1778
100 = 0.1397
120 = 0.1168
200 = 0.0737
325 = 0.0432
400 = 0.037
625 = 0.020
1200=0.012
2500=0.005

Break-Down Temperature of Common Mould Binders

The temperatures that various binders used in mould making is important to consider, as once they reach the break down point, they lose their strength and therefore ability to hold the mould together. The following table gives some indication of the characteristics of various binders.

Binders and Break-down Temperatures (degrees C)
Gypsum plaster - 704 - 816
Hydrocal cement - 704 - 816
Hydroperm cement - 760 - 927
Colloidal silica - 1260
Colloidal alumina - 1260
Calcium alumina (ciment fondu) - 1538

These of course, are not the only considerations in mould making but do show why combinations of materials is important. The common plasters and cement break down before the casting temperature of glass, typically 850C.

Polishing 3D Glass on a Wet Belt Sander

Polishing three dimensional objects depends on the shape of the glass you are sanding down to the polished surface.

Convex shapes can be done on the wet belt sander with ease.

You can polish slightly concave items on a belt sander if you have an unsupported section of the belt. On machines with a flat platen, you can remove the platen to use the ability of the belt to form into a slightly convex curve.