Color Cement Handicraft 4

Color Cement Handicraft 4

THE DESIGNS FOR INCISED PATTERNS are best where the lines enclose a

shape. The parts are more comprehensive and confusion of the lines will

not result if simple outlines are used. In the chapter on Design, line

patterns are shown that are adaptable to incised work.

 

TO INCISE THE PATTERN take a nail point or nut pick or other metal point

and shape the point on a grindstone or by the use of a file so that each

incised line will have a tapering side. If any undercuts are produced

the cast or plaster that is poured into it will become locked and refuse

to separate.

 

The tile is next immersed in water, taken out and after the water is

absorbed, a brushing of oil is given to it.

 

A PLASTER TILE IS MADE MORE DURABLE if it is dried and given a coat or

two of shellac before it is used for molding plaster or cement.

Otherwise repeated brushing of damp plaster with the oil brush will

gradually wear the edges and details of the mold away.

 

TO MAKE A CAST FROM THE PLASTER MOLD, it is surrounded with the

retaining bars after they have been oiled and held in position with the

modeling wax or clay; this time they are placed firmly against the sides

of the plaster mold.

 

THE CAST OF OUR FIRST EXPERIMENT now becomes the mold for our second

practice problem as the mold is always the part that produces the cast.

The cast in turn may become a mold for another cast.

 

TO SEPARATE THE CAST FROM THE MOLD the bars are removed and a knife edge

is pressed between the parts to separate them. Care should be taken not

to become too anxious and force the sections apart before the cast has

dried or they will cause it to break. If it refuses to come apart easily

when completely dry, a little wooden wedge tapped into the crevices in

one or two places will cause it to part easily. Sometimes plaster flows

over the sides of the mold and binds the edges together. On removing the

mold and cast from the retaining bars, examine it to see if any plaster

is binding it and if so remove it.

 

IF THE PARTS ARE ABSOLUTELY SOLID it is because the incising was not

properly done and the lines interlock somewhere and the only thing to do

is to break them apart and correct the faults and try again. Sometimes

when interlocking tiles are separated the faulty parts have fragments of

the opposite part attached in the defective parts showing where the

faults are located.

 

THE TWO PLASTER TILES SHOULD BE RETAINED for they can be used in casting

plain cement and color cement tiles in various finishes. When they have

completely dried they should be given two or three coats of thin

shellac, a day apart, on the surface only, which will make them good

durable molds for future use.

 

CASTING IN THE ROUND is more difficult than flat casting or bas-relief

work and while the making of plaster molds for vases and bowls is given

particular attention in the chapter on Cement Bowls and Vases,

directions for casting objects in the round will be given here.

 

AS A GOOD TEST PROBLEM take any small object or toy and, if it is wood,

oil it well. If it is porcelain or glass it will not need to be oiled. A

simple form, animal or bird, can be made in modeling wax or clay to be

used as the original or model from which to make a mold. The best

objects are those modeled in broad surfaces with but little detail.

 

PREPARING FOR CASTING. The equator or half-way mark should be marked on

the surface of the object, as one-half of the mold should be made at a

time. Instead of one-half, one-third is often used on round objects to

permit easier release of the molds. Mold divisions when possible should

follow corners of objects.

 

THE FIRST SECTION of the mold is made by placing a layer of clay along

the division lines on the object which have been indicated as division

lines for the sections of molds. Sometimes the object can be laid on the

table or on glass and the plaster poured around it up to the half-way

line as shown in the accompanying plate. In this method a strip of

linoleum or metal can be placed around it to make a retaining wall for

the plaster.

 

AFTER THE FIRST SECTION is cast, the model is removed from the plaster

and if the plaster has risen past the equator it should be scraped back

and indentations or “keys” made in the plaster portions that are not

those producing the parts of the model. The model is replaced in its

hollow and the entire surface of the mold that is exposed is oiled,

including the sides of the metal, linoleum or whatever is used as

retaining walls. Plaster is again poured for the second half after which

it is permitted to dry before separating the mold sections.

 

OILING. It must be remembered that the molds must be oiled after each

casting as each pouring absorbs the oil. All surfaces coming in contact

with the next pouring of plaster must be oiled to cause separation.

 

POURING. A hole must be cut in the molds to permit the plaster to enter.

Air holes leading upward as shown in the engraving are scraped upward

out of the molds to permit the escape of the air; otherwise air bubbles

may be formed in the plaster causing defects.

 

TO HOLD MOLD PARTS TOGETHER tie a cord or wire around parts. Notches cut

on corners or edges of molds to hold the tieing cord will prevent them

from slipping. Molds should fit closely together. If for any reason they

do not, the crevices can be filled with modeling wax as a temporary

filler. The best results are obtained, however, from perfect molds and

it is a saving of time to make a mold over if it is not perfect in the

first casting.

 

RELEASING CAST. After the plaster has set long enough to harden, the

molds are opened by gentle prying or tapping with a wooden wedge. Often

an obstinate cast is released by placing the mold over a stove or flame

for a few seconds. This causes the steam formed in the mold to separate

the mold from the cast.

 

CEMENT BOWLS AND VASES are made by pouring thin cement into the molds

and rotating the mold and pouring out the surplus cement. After a few

minutes another layer is poured in and the operation repeated. This

method is explained more fully in the chapter on Bowls and Vases.

 

[Illustration: The Making of Plaster Molds]

 

[Illustration: The Making of Molds]

 

 

 

 

[Illustration]

 

CHAPTER 3

 

Plain and Incised

 

Cement Tiles

 

[Illustration]

 

 

A KNOWLEDGE IN MIXING CEMENT is the next step necessary in Color Cement

Handicraft. The steps necessary toward mixing cement are simple, the

main point being that the cement should be fresh. The student is

cautioned to test the freshness of cement by seeing that no caked or

hard lumps of cement are contained in the sack mixture. As formerly

explained the cement should have a smooth, slippery feeling when passed

between the fingers.

 

NEAT CEMENT is the term applied to cement mixed with water without the

addition of any sand or gravel. Neat cement produces a very smooth

surface and responds to reproducing every change in the surface of the

model. It should be used on the surface only and not for the entire tile

or pottery. If used without any sand or gravel, it is termed “too fat,”

and has the fault of cracking sooner or later. Therefore neat cement is

always backed up with a concrete mixture.

 

CONCRETE is a mixture of sand and cement, gravel and cement, or rock and

cement. In all instances where such a mixture is made, the two parts

should be _mixed dry_ before any water is added. Only enough should be

mixed to meet immediate needs as it is not best to use cement that has

stood so long that it has commenced to harden.

 

TO SECURE A VERY FINE SMOOTH SURFACE for tiles or pottery the cement

should be used neat. It must be sifted dry through a fine sieve and

enough water added to make it of easy working consistency. Then a

mixture of two-thirds gravel or sand and one-third cement with water

added may be used on the back of the tile or the inside of a vase and

possibly again lined with a mixture of neat cement.

 

Cement or concrete can stand for an hour or two and again be used by

adding more water and mixing thoroughly. This cannot be done with

plaster and should be avoided with cement or concrete. If chemical

action has commenced and the cement has partly set, it naturally will

have lost much of its strength for second use.

 

A CONCRETE MIXTURE of one part cement and two parts sand or gravel will

give good strength. The sand or gravel must be clean. If it contains any

vegetable matter or other sediment, it should be avoided. To test your

sand quality put a four-inch layer in an ordinary quart jar, fill with

water within three inches of the top. Cover and shake well. Then permit

the sand to settle. If the sediment or loam which remains at the top of

the sand is one-half inch or more, the sand is not fit for use in

concrete.

 

CEMENT MIXTURES ADAPTABLE TO VARIOUS USES are given below. These may be

used for backing and reinforcing large problems, in garden pottery,

garden furniture or walls.

 

1. RICH MIXTURE

1 part cement

2 parts sand

5 parts gravel

 

2. STANDARD MIXTURE

1 part cement

2 parts sand

4 parts gravel

 

3. MEDIUM MIXTURE

1 part cement

2½ parts sand

3 parts gravel

 

4. LEAN MIXTURE

1 part cement

3 parts sand

6 parts gravel

 

 

Cement and sand mixed dry first, then with water. The gravel is mixed

wet with other mixture and thoroughly combined.

 

Builders use the Rich Mixture for columns and high stresses, and where

water tightness is necessary.

 

Standard Mixture is used for arches, for tanks and sewers, and for

machine foundations.

 

The Medium Mixture is used for piers, sidewalks, and heavy walls.

 

The Lean Mixture is used for walls, foundations and for unimportant work.