Oleh: arkeologibawahair | 27 Mei 2011

Experimental Cleaning on Ceramics Results of Underwater Archaeological Excavation*

By: G u n a d i K.

Historical and Archaeological Service of Makassar, Indonesia

I. Introduction

Until now, research on underwater archaeology in Indonesia less than the other countries. The last two decades working at underwater archaeology was stagnant, especially since Mr. Santosa Pribadi was die when he got diving at Riau Islands. He is one of Indonesian archaeologist who pioneer to study underwater archaeology. That is why to covered stagnant above, since last year the Historical and Archaeological Heritage Service of South and Southeast Sulawesi Province try to develop about underwater archaeology in East Indonesia Region. We prepare about human resource and also try to working at underwater archaeology likes survey and excavation at surrounding Makassar Strait. Result of that survey we found several location as a potential underwater archaeological sites.

Basically, underwater archaeology and terrestrial archaeology both have same methods and theories (Soeroso, 1997 : 4). But underwater archaeology needed special skill, that is diving, so only few archaeologists want to study about it. In Indonesia activities of underwater archaeology still focused under the sea, then the research target are shipwreck sites and usually the ships cargo are ceramics. But all of the ceramics nearly was overgrown with coral-reef which very difficult to removed. Conservation method to remove the coral-reef from the surface of the ceramic, generally the conservator drops on ceramic surface with 0,5-1% of Chloride Acid in aguades (Sadirin 1997 ;16-18), and our experiences by using that chemical was really a worst cleaning results. It is a big problem how to remove the coral-reef was overgrown on ceramics. O.P. Agrawal in his book entitled Care and Preservation of Museum Objects said that to clean ceramic from shipwreck sites is soaked thoroughly in running water or in frequently changed distilled water, until completely free of salts (Agrawal, 1978 : 69), but he did not say further how to removed coral over ceramic surface.

How to over come the main problem above, our conservation laboratory try to several experimental cleaning on ceramics results of underwater archaeological excavation. We have three kinds of experimental cleaning, first is boiling in aquades, second is heating by oven, and third is put in air keras formulation. Air keras is local term addressed to call a chemical composition of sulphate acid (H2SO4).

II. Kinds of Experimental on Ceramics Cleaning
Two experimental cleaning are boiling in aquades and heating by oven suggested by physical theory which is called that anything compact material put in heater will be expansion. Expansion differences process between ceramic and coral-reef or other material overgrown on its surface, cause the released of same materials mentioned. While for chemical experimental cleaning by element of sulphate acid suggested from Makassar Antiquarians Association. The third process of experiment as follows :

1. Boiling in Aquades
The sample of artifact in cup of bowl as the results of underwater archaeology excavation at Bulango site, Makassar strait. Before conservation, almost all ceramics surface covered by coral, red algae, and molusca. The boiling procedure, as follows :

a. Prepare pan and fill it by aquades as enough
b. Put ceramic into the pan till all parts of it soaked
c. Boil till reach 1000 C for 2 hours
d. Take the ceramic out
e. Removed the remaining coral by using spatula.

The observation results of boiling technique can be known that changing colour isn’t happened, the glaze layer isn’t ruined or having shabby and physically the crack isn’t happened. But there’s still fat remaining which is very thin and hard to be cleaned.

2. Heating by Oven
Heating by using oven is inspired by the results of boiling experiment above by considering that oven using can be increase its head temperature. The sample of this experiment is fragment of ceramic from underwater archaeological site of Bulango. Almost all surface covered by 80 % coral remaining, 13 % red algae and 7 % molusca. The heating procedure by using oven as follows :

a. Put the sample in electric oven
b. Heat it on 1000 C for 30 minutes
c. Increase the temperature till 2000 C for 30 minutes
d. Let the sample out of oven

The result of the experiment above such as, the dirt of coral, red algae or molusca which stick on the ceramic surface can be easily released without ruin the glaze or the surface of ceramic mentioned, even there’s one part which is directly separated by itself. Changing colour of ceramic’s glaze isn’t happened and physically there is no crack. The second experiment technique above is done based on the way of making ceramic which uses heat till reaching over 10000 C temperature (Marimoto and Yamasaki, 2001 : 15), then if the ceramic heated till 2000 C, then it’s predicated physically there is no changing happened. Like the boiling process above the fat remaining which is very thin still left on ceramic surface and hard to be cleaned.

3. Put in Air Keras Formulation
Air keras is actually the local term which is usually used by the antique traders in Makassar, South Sulawesi. The chemical mentioned is a pack which can be bought in a chemical store in Makassar. Based on label in a pack is known that the containing or the material composition is :

– Sodium hydroxyde 15 gram/1 litre
– Ethyl N-2- Methanesulfonil Aminothyl 50 gram/1 litre
– Methylpenilen Yamine Sesquisulfate Monohydrate 159 gram/1 litre
– Pottasium Carbonate

The cleaning by chemical materials above is treated on those two samples which have been cleaned trough boiling or heating by oven. This thing is done because the result of the two experiments above is not got rid of all the fat remaining.
The conducting procedure which worked by Makassar antigue traders as follows :

a. Soak the ceramic artifact into 100 % of air keras formulation for 24 hours
b. Washed by water
Really, coral, algae, and fat remaining can be disappeared and the colour of ceramic looked clean.

After doing observation microscopically, there was a change of glaze layer. To know how the effective and efficiency the air keras formulation above, than we did some experiments by stretching air keras in aquades. The solution disposal is differed in some kinds there are : 1 %, 5 %, 10 %, 25 %, and 50 % which each solution above is applied in different time.

The result of the experiment above as follows :
– The ceramic is soaked in 1% of air keras formulation in aquades for 24 hours, the result can not be released the coral which is over the ceramic.
– The soaked of ceramic in 5 % of air keras formulation in aquades for 24 hours has succeeded remove the coral, molusca or even other dirt over the ceramic surface.
– 10 % air keras formulation in aquades and the soaked of ceramic are done for 6 hours, coral, molusca and other dirt can be released, but there was a change happened over the glaze layer because of the scraped of H2SO4.
– 25 % air keras formulation in aquades by soaking the ceramic for 2 hours, the scraped which has happened over the glaze layer is deeper.
– 50 % air keras formulation in aquades by soaking the ceramic for 2 hours, the scraped of glaze layer is stronger then the ceramic surface looked isn’t bright.

III. HCL Formolation in Comparative Method
The formulation of HCL (Chloride acid) is between 0,5 – 1% in aquades as conservation of the invention of ceramic is formulation which often be found by the Indonesian conservation expert. But, in the fact the use of 1% HCL formulation in aquades which has been applied on the invention ceramic from under water excavation by us, whether by applying technique or soaking, the result is half of coral and molusca which is over the ceramic surface is still hard to be cleaned.

HCL is chemical form which is destructive for material such as ceramic. Because of that we didn’t do another experiment by adding more of HCL, because we worried would damage the glaze layer. Refer to this comparative results, than we did such experiments as what have been mentioned in the previous chapters.

IV. Closing and Recommendation
The underwater artifacts invention in Indonesia, most ot them from shipwreck sites which were from XVI-XX centuries. The ship cargo was ceramic, after years in the ocean they were usually grown by coral, algae, or other micro biology which was cause the discrease of ceramic quality. The ceramic surface which was easily grown by coral, because both of them consist of same material that is calcium, then both of them are easily to be one. As has been mentioned in the first chapter above is very serious problem concerned to conservation method, that is how to clean coral, algae or any other dirt over the ceramic material as the result of underwater archaeology excavation.

Some experiments by conservation method on ceramic over the underwater archaeology excavation invention which was done by Archaeological and Historical Heritage Service of South and Southeast Sulawesi Province, there were boiling, heating, and soaking in chemical formulation. These are innovative steps to solve the big problem above. Among those three kind of methods above, can be divided into two, there are mechanical cleaning and chemical cleaning.

The boiling method and heating are ways without making negative impact, and the result is close to perfect but it leaves the very thin fat which hasn’t been cleaned by those two methods above. The conservation experiment method by using one of chemical formulation is a composition which contain sulphate acid (H2SO4), even though it has been found a formulation considered most effective, but still we worried on the negative impact which is cause by the chemical reaction.

Based on the result of several experiments above than conclusion that we recommend as follows :

1. Mechanically, the boiling and the heating method are the most effective and efficient methods and they don’t cause negative impact.
2. Chemically, the soaking method of 5% air keras formulation in aquades for 24 hours is the most effective method with lowest negative impact.

As the closing I need to say that we keep on doing the other same experiment, especially in how to clean the fat layer which is still remain from the boiling and heating results without damage or discrease the glaze layer quality over the ceramic surface. Our great expectation is hopefully those experiments which we have done will be advantage to the development of conservation method for the underwater archaeological objects in Indonesia.

The experiments of ceramic cleaning results of underwater archaeological excavation could be done because of a good teamwork between writer and our laboratory staff, and the willingness of my friends from underwater archaeology section who have given some fragments of ceramic to be our experimental objects.


Agrawal, O.P. 1977. Care and Preservation of Museum Objects. Published by National Laboratory for Conservation of Cultural Property, New Delhi, Printed by the Manager Government of India Press.

Marimoto and Yamasaki, 2001. Technical Studies on Ancient Ceramics Found in North and Central Vietnam, Published by MARIMOTO Asako, Printed by Sei-un Printing Co. Kitakyushu, Fukuoka, Japan.

Sadirin, 1997. Teknik Konservasi Benda Cagar Budaya di Museum, Diktat Acuan bagi para peserta Penataran Tenaga Teknis Permuseuman tipe dasar, Direktorat Jenderal Kebudayaan, Departemen Pendidikan dan Kebudayaan (unpublished).

Soeroso, 1997. Ekskavasi Penyelamatan Arkeologi Bawah Air, Diskusi Ilmiah Arkeologi di Jambi, Ikatan Ahli Arkeologi Indonesia, Komisariat Daerah Sumatra (unpublished).

*) Makalah dikirim ke ‘Asia – Europe Seminar on Cultural Heritage Training’, University of Alcala, Madrid, Spain, 26 – 29 November 2001.

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